Trained Bears

Trained bears were have been a popular source of entertainment in the Middle Ages and Renaissance.

Bears seem to be the most frequently-depicted trained animals in the period iconography, but there are a few trained dogs as well (such as this lead token of a man with a trained dog, France, 15th century). Martin (in Alcohol, Sex, and Gender in Late Medieval and Early Modern Europe) notes that "keepers [of taverns and alehouses] procured dancing bears, jugglers, and minstrels to lure the young men and women to come and have a drink" (p. 76); trained bears also sometimes appeared at fairs and festivals, as described by Alvarez (in Juggling - its history and greatest performers):

The trained bear was led away and the jugglers entered. A man and a boy. They carefully unfolded their bags and began performing. The man, running around in small circles, rapidly juggled with three knives. The boy, whip in hand, would at times, in jest, castigate the man whenever he fumbled. The effect was dexterous, comical, and most entertaining. After the older minstrel had walked on his hands and juggled with balls, the pair collected some coins, folded their bags, and calmly walked away to disappear into the mob. The singers now entered with their music scrolls in hand.

A very different story of a dancing bear comes from the Thiðrekssaga (or, in German, the tales of Dietrich von Bern), in which Vildifer (Wildeber) rescues Vidga (Wittich) with the help of the minstrel Isung (as retold below in Legends of the Middle Ages):

Wishing to penetrate unrecognized into the enemy's camp, Wildeber slew and flayed a bear, donned its skin over his armor, and, imitating the uncouth antics of the animal he personated, bade the minstrel Isung lead him thus disguised to Hertnit's court.

This plan was carried out, and the minstrel and dancing bear were hailed with joy. But Isung was greatly dismayed when Hertnit insisted upon baiting his hunting hounds against the bear; who, however, strangled them all, one after another, without seeming to feel their sharp teeth. Hertnit was furious at the loss of all his pack, and sprang down into the pit with drawn sword; but all his blows glanced aside on the armor concealed beneath the rough pelt. Suddenly the pretended bear stood up, caught the weapon which the king had dropped, and struck off his head. Then, joining Isung, he rushed through the palace and delivered the captive Wittich; whereupon, seizing swords and steeds on their way, they all three rode out of the city before they could be stopped.

I suspect that this story is a later addition to the saga, rather than a literal episode from the lives of the companions of Theodoric the Great (on whom the Thiðrekssaga is based), but there is certainly plenty of evidence that trained bears were known in Ancient Greece and Rome.