the.com/bull

means A person who bets markets will rise, buying now in the belief prices are headed up — also, by extension, the general term for upward market momentum.

from The origin is genuinely murky. By the early 1700s 'bull' and 'bear' were both in use on the London stock exchange for optimists and pessimists, but nobody recorded why those two animals. The most repeated explanation links 'bear' to the old proverb about selling the bearskin before catching the bear (a bear-speculator sells what he doesn't yet own, betting the price will fall), with 'bull' picked up afterward simply as its natural animal opposite — bulls thrust upward with their horns, bears swipe downward with their paws. It's a tidy, memorable story, but etymologists treat it as likely folklore rather than documented fact.