There is a barrow where you can find multiple werebears at once. The werebear is a monstrous bear-like creature.
Actually, there are many werebears, but they do not appear in the main quest.

Fighting a werebear is not easy, but you'll need a follower with you to fight the werebears. The werebears are berserkers. Once they are not in lycanthropic form, it is easy to hit the werebear. Note that Stalhrim weapons are also required. They are from Snowclad Ruins. If the werebear dies if you have a Stalhrim weapon equipped, loot the werebear.