Biography
Want to make a bad situation worse? Add a bear!
Just as monkeys are used to make something funnier, bears have a knack for scaring the crap out of everyone. Polar and brown bears are the largest extant land-based predators in the world, with a penchant for aggressive behavior, so it's easy to see why.note Because of this, throwing a bear into a scene is the best way to let the audience know that our heroes have gone beyond rock bottom and are now totally screwed.
In many a film and television show, our heroes will quite often find themselves cooped up in a cabin as a killer bear is just outside, trying to get in.
This can sometimes be Truth in Television. Being between a mama bear and her cub has been justly described as the most dangerous place on earth, but any number of bears can be very dangerous indeed.
Another issue is that bears are very intelligent (often regarded as being very close to chimpanzees) and they actually have individual personalities. This adds to their unpredictability as to how a bear reacts to a certain situation will entirely depend on both the bear itself and the mood it's in at the time.
Bears have such a long history of scaring the Pooh out of human beings that most of the names we've ever given them are derived from conciliatory euphemisms, as part of an old taboo against naming something so dangerous. The English word 'bear' originally meant "brown one", and the Slavic word medved originally meant "honey eater." Even the original Proto-Indo-European word was related to the word for "destruction", proving just how ancient this particular Primal Fear is.
Incidentally, this same fear has also inspired great respect, as such, a great way to raise the credentials of any badass, villain, or Anti-Hero if you give them a bear. Especially as a mount, because there's nothing cooler than riding a bear... except maybe a robot bear or zombie bear, or a bear made of fire or ice...
Ursine Aliens can also invoke this.
Do not confuse this with The Bad News Bears (the Trope Namer, though not an example), with the Bearer of Bad News, with The Bear, which is about a big hairy Manly Gay guy, or with Exit, Pursued by a Bear, though that trope's name is an example of this trope. In the Land Down Under, you should watch out for drop bears, though those are supposedly carnivorous koalas rather than actual bears — but even real koalas can be plenty dangerous in their own right, being Australian Wildlife and all. Mama Bear may be related but is usually metaphorical.
For animals that tend to get a similar treatment, see Savage Wolves, Cruel Elephant, Rhino Rampage, Maniac Monkeys (and Killer Gorilla), Threatening Shark, and Reptiles Are Abhorrent (and Never Smile at a Crocodile). Often a Super-Trope to Fighting Panda, for when pandas are portrayed as martial artists capable of kicking ass.
Contrast with to Pandaing to the Audience, Beary Funny and Beary Friendly, which are about more positive depictions of bears.note