Geniuses who were just insane

Lord Byron, English poet, 1788-1824:

It began when Byron arrived at Cambridge, where he was ordered to send his dog back home as keeping one was against school rules. Desperate for a pet, Byron scoured college policies for an animal not expressly forbidden. He found no reference to bears.
The bear stayed with Byron in his dorm room. Being a responsible pet owner, Byron took it on regular leashed walks through the university, terrifying fellow students and lecturers. When asked by administration what purpose the bear served on campus, the poet tried in vain to get his beast a fellowship.

More here (including Newton).