The best knife for defense against a large predator is a midshipman's dirk, because it means you're commanding a cannon crew. From a boat.

I think I would choose a letter opener. You see, if I had a fancy letter opener, I would want to use it all the time. Thus, putting me in my office instead of out in the wood with the bears.

I'm just here to check if he is still Matt Easton.

As someone that has hunted for well over 40 years and have very much knowledge about animals like wild boars, bears and many many others, and having experienced a few attacks, do I have a few comments about this.
First of all is a 4 inch blade close to useless to use in defence against most of the animals that might attack you.
6 inches is the minimum and even if that can be a bit short against animals like big wild boars, male lions, tigers and brown bears, does it work well against animals like dogs, black bears, cougars hyenas and smaller wild boars.
You need to reach deep enough to do enough damage to vitals to incapacitate the attacking animal as quickly as possible.
To just tickle a vital organ with just an inch of your blade can make it take way to long before the attack stops.
The more damage you do to one or more vital organs, the quicker it takes.
And seconds can be of extreme importance if you experience an attack.
An ideal blade length for the larger animals, is 7 to maximum 10 inches in my opinion
Personally I prefer 7.5-8.5 inches.
Long enough for everything and not longer than needed.
Anything longer than 10 inches is pointless and can often be counterproductive.

Of the knives you showed, then the Muela is the closest to what I consider to be an ideal self defence knife against animal attacks.
I think some sort of hunting/fighting dagger where the blade is 5mm thick at the thickest, 40-50mm wide, 7.5-8.5 inches long and a similar blade profile to that Muela is perfect.
I prefer to have both edges sharpened all the way down to the guard and they need to be razor sharp as it is VERY important that the knife/dagger slides as easy as possible in and out as you might be in a position where it can be hard to use much force.
And by having the edges very sharp, you can also cut very easily if that is needed or the best solution.
It is important to have a grip where you have full control of where your edges are and that you can use both an icepick grip and a hammer grip very well.
The grip needs to have some sort of solution at the back to avoid your knife/dagger to slip out of your hand when you draw it or pull it out after you have stabbed with it and it is also great if the grip has some sort of texture that makes it easy to get a good hold onto it even if it gets wet from sweat, water or blood.
Some have very well textured grips, making it not needed to have some sort of pummel or larger "diameter" at the back end to avoid the knife/dagger slip out of your hand.
This is typical of some of the synthetic grips that are on daggers, knives and even some swords today and this is the type of grip I prefer even if it doesn't look as good as other grip materials.

The Cold Steel Tai Pan is an example of a good design for a self defence knife/dagger against dangerous animals.
I am no fan of the sheath and when considering the  price, then the sheath should be much better in my opinion.
But the point is not the brand or the exact knife/dagger or the price, but what type of blade profile that works very well.

There are many similar blade designs that are very good, but way to often is the grip and/or sheath lacking in my opinion.

I have needed to defend myself against animal attacks with a knife 3 times in my life.
A large wild dog, a warthog and a medium sized wild boar.
Only the medium wild boar managed to injure me a bit with a small cut.
Most likely would I have managed as well with a knife/dagger with a 6 inch blade, but I didn't regret that I had a 7.5 inch blade.

The chances of surviving an attack from a lion, tiger or a polar bear with only a knife/dagger for defence are EXTREMELY small, but they are still higher than if you don't have that knife/dagger.
Those animals usually attack you because they regard you as food and they do not hesitate or play much with you and they are extremely strong.

Your chances against a brown bear with a knife/dagger are not high, but they are not to bad either.
Often brown bears take a rather long time to dispatch you and this is specially the case if it is an attack that is not motivated by hunger.
A friend of mine is a bear expert and he has done research on bears for decades and once he and a colleague experience to be attacked by a brown bear and my friend shot the bear with his colleague's 44 magnum that his colleague managed to drop on the ground because he fumbled to draw it from the holster in full panic as the bear charged him.
And my friend was so "smart" that he had brought no gun or knife with him, so he had to get the gun from almost underneath his colleague that had the bear on top of him.
It took a rather long time from the bear charged till my friend put a bullet or five in the brain of the bear and still his colleague was not that badly hurt and he had in reality "much" time to defend himself with a knife if he had one on him.
My friend has learned from that time and since then has he always had 3 weapons with him when out in the bush on bear country.
A shotgun with slugs, a 10mm Glock and a hunting dagger with a 9 inch blade.

Against black bears, cougars, leopards and a single hyena are your chances rather high if you are an average sized man that is not to weak and you know what you are doing and don't panic.
Against a single dog, a single wolf and a medium to small boar are your chances very high if you know what you are doing.
Yes, you might get injured, but the chances of you dying are very small.

Against large wild boars can it be a matter of good or bad luck and it is one of the animals I am the most stressed about tracking if it is wounded by a hunter.
They are big and very strong animals and they can have very long and razor sharp tusks, so they can quickly do a lot of damage and they can very quickly and easily cut off your femoral artery and if that happens, it is goodnight in seconds and no knife will help you.
They are also much harder to grapple against because of how they are built compared with other animals
The fight I had against the medium boar was a proper challenge before I managed to dispatch it with my hunting dagger and I am not sure how it would have ended if it was a proper large boar.
It managed to knock the gun out of my hands before I got time to shoot it as it attacked me from under a thick spruce while I was following it's blood with a tracking dog after a hunter had wounded it.
The dog was a wirehaired dachshund, so it was not exactly big enough to fight the boar, even if it tried to help me as they think they are the same size as an elephant and scared of nothing.

Sorry for the long essay, but I hope at least one or two thought a bit of it was of interest and helpful.

When I read the title, the first knife that came to my mind was the Arkansas toothpick

I actually have a relevant comment about this topic. The Ontario Ministry of Natural Resources updated their bear safety recommendations for staff doing backcountry work about 15 years ago and one change was to recommend that belt knives have a blade of 6 inches in response to the particulars of a recent (at the time) black bear attack in NW Ontario in which a knife was used in defence. Normally bear spray is the main direct deterrence but this occurred when a crew of two OMNR staff left their spray in the truck while making a short foray to do something (I don’t recall what). They split up and a bear began stalking one crew who was a young woman (small people are more likely to get attacked). She radioed for help and tried to work her way back to the truck but didn’t make it before getting knocked down and attacked. Her partner arrived to find her being mauled and chased the bear off but it returned and charged him several times to try to get its prey back. The partner stood over her and used his belt knife to fend off the bear. I don’t remember how exactly they got to safety but they did and both were ultimately OK but the woman had some fairly serious injuries to her back and shoulders (she was able to protect her face and neck). Anyway, the bear was later killed and necropsied and it was discovered that the 4” knife had not penetrated beyond the subcutaneous fat. So updated guidance is a 6 inch blade and don’t leave the bear spray in the truck.

Edit: People keep replying to me about legality of weapons for some reason. In Canada, you are not legally prohibited from carrying bear spray and a belt knife in the woods. If you can walk into any Canadian Tire store or Cabella's and buy it, it's probably not illegal in Canada. So, my first piece of advice is to go touch grass and stop getting angry about fake stuff you imagined or saw on tic toc. I am not a lawyer but as far as I know, and I've never had issues following this: in Canada you are generally not allowed to carry something that is reasonably interpreted as a weapon against other people. Saying it's for self defense (against other people) doesn't matter. But if you have it for a legitimate purpose in an appropriate context then you're good. If you have an axe in the woods you're fine. If you bring an axe into a shopping mall you're not. If you're hiking in bear country you can carry bear spray, but don't bring it into the post office. If you're in your kitchen you can have an 8" chef knife but don't walk into an elementary school with it. If you're trying to push the line to see what you can legally get away with don't ask me, I am not that interested in that stuff. Common sense goes a long way.

James Bowie's older brother, Rezin - is generally credited with the original concept of the Bowie knife, albeit the early Searle's style.
He was attacked by a bull & used his large belt knife to kill it.
The bull had him pinned (against a pasture fence, if I recall correctly).  However, his knife didn't posses any kind of guard & his hand slid up the blade as he tried to stab into it's brain, severely slicing his fingers' tendons.
He finished by literally pounding the pommel with his fist to drive the blade home.
During his recovery he designed a blade which dropped below the hilt, giving a knuckle-sided stop guard to protect the hand from progressing forward during hard stabbing actions.  This is commonly called the Searle's style Bowie.
Both Rezin & Jim had been taught sword fencing as children & Rezin began modifying his initial design over the next couple of years.  This is where the quillon cross guards began to be incorporated into the Bowie Knife design.
Rezin then gave one of his blades to his brother, Jim, when Jim started to receive threats against his life from other folks in the area.
Still thought to be a Searle's style - straight spined - blade but with some kind of cross-guards, although it may have been what is now referred to as a Musso Style, or early iteration of it - that was the knife Jim Bowie carried & used during the Sandbar Duel.

Jim was severely wounded during that fight, although he survived & his sword wielding attacker did not.  Much like Rezin had used his recuperation time after killing the bull, Jim used some of his recuperation time to refine the knife's design - including MUCH LARGER GUARDS - and a forward extension to the guard's ends became a critical component in Bowie's future designs for trapping an enemy's sword or knife blade.

He also began to reduce the length of the blades - down from around 13" to his final acknowledged design - the Bart Moore Bowie - with an 8 & ½" or 8 & ¼" blade - double forward hooked guards and an inset strip of soft brass along the spine of the blade, to further enable capturing an enemy's blade.
The clipped point design was intended, as Bowie said himself, "...to pierce like a dagger, slash like a scimitar and chop like a cleaver"!

Bowie used his blade in an edge-up saber-style grip - this put the brass strip down, toward the knuckles.  He was famously good at catching an opponent's blade, forcing it down; across the body toward his enemy's left side, grabbing the opponent's forearm as he disengaged his knife & then instantly ripping his edge-up blade into his enemy's guts & up into the heart & lungs for an almost instant kill.

Just an American's Historical Four Hae-pennie's worth!

Keep up the great work, Matt!
👍👌🖖🤺

When I lived in Anchorage, Alaska, a man in the city heard a crash and went downstairs to find a bear had broken into his living room through the patio door. He ran the bear off with a sword. Unfortunately, the news article didn't provide any information about what type of sword it was. I think this was around 2006, but it's been a long time and I may have the year wrong.

The seax's lack of handguard scares me.

Not a kirpan...

"Three weeks later, a Sikh Jemader (supervisor) named Ungan Singh was seized from inside his tent by a lion in front of horrified workers. The following morning, Patterson went to the scene and came across several pools of blood. When he stumbled across Singh’s corpse, nothing remained except scraps of flesh, several bones and the largely intact head of Ungan Singh who died with such a terrified grimace on his face that it traumatized Patterson"

The K-Bar knife trademark comes from a Union Cutlery Company knife being used by a man to save himself from a bear in Alaska.

Don’t forget the dogs that run wild in some cities.

so i was going up to SE Alaska to help a friend clearcut a large part of a property he had just bought so he and his family could homestead it, so i figured i would make a big knife for the trip to carry in case i ran into a bear (i didn't own a handgun att.) so i made a big Scottish dirk out of some 1090, clay hardened the blade so it has a beautiful hamon line, notched filework on the spine, brass fittings, the handle is some big leaf maple branch from my backyard that i ebonized with a blowtorch, it's a beautiful knife, and i would sleep with it in my right hand or tucked into my left armpit every night i was there.
so the logging trip is coming to an end, i'd been sleeping in a little one man backpacking tent for a few months without any sign of big wildlife (makes sense, we were running chainsaws all day everyday) and i'm laying down in my bedroll texting my mother when this big black dog sticks its head in the door of my tent right over my own head and starts sniffing around, and i'm laying there looking up at this big black beast going "whos fucking dog is this?" then my brain puts two and two together and i realized a few things, one: it was not a dog, i was in smooching distance of a black bear, and two: i had absolutely no idea where my knife was...
so i dropped the phone and threw the hardest uppercut punch of my entire life right into this bear's nose.
it worked, the bear must have been as surprised as me because it made fast tracks and left me alone and roaring as loud as i could in my tent with that knife now "magically" in my hand.
i figure i'm alive today because A) it was a black bear not a brown bear B) it wasn't really that hungry, my beautiful knife has nothing to do with it.

The best type is whatever you can put on a stick to make a spear.

I have never thought about carrying a knife for defence while hunting, but almost two years ago while hunting wild boars with my uncle did he get attacked and he reached for his knife a Mora Garberg and managed to stabb the boar before I could safely shot it, after that incident we decided to get us some knifes better suited so I looked around after some large knifes like a Bowie and a guy on some knife forum recommend a BeggKnifes large Filoso which is a 35cm long and 4cm wide dagger. So I bought two one for me and one for my uncle so now do we both feel a little more safe hunting boars.

Assuming you can’t have gun or you missed or it’s malfunctioned and out of the fight.  4” probably isn’t enough to reach the vitals of a Bear or other large predators. 6-8 is probably more likely to actually reach vitals
You probably should choose a larger 8-12 inch blade with a diamond cross section and a significant guard and robust grip and pommel. So a rondel dagger would probably work or a d guard Arkansas toothpick. Or a d guard large Bowie with the false edge sharpened

The tiger is packing 20 switchblades so I still don't fancy your chances.

50 years ago, when I lived in Idaho, USA, and was an avid deer, bear, elk, and coyote hunter; and a predator control hunter for some grange associations? The knife I always carried on my belt was a Buck Model 124 Frontiersman. A full tang, 6.25" bladed Bowie-style knife. It was only ever used as a camp chore knife - fortunately - but, it was perfectly capable of saving my butt if necessary. Still have it, too...

Using a knife against a bear is really a plan F when avoiding and your primary deterrent fails. With that said, it’s better than your bare hands.

The content of this channel is pure gold.