There's quite a few people who get involved in Jake's adventures, often in an attempt to curtail his destructive tendencies. Here's a few of them.
Jake the Evil Hare, of course
Nadine, his friend and roomate
Ethel the late-working secretary at the Burpy Building
Peter Ferguson - a certified uber-nerd
The Alpha Male - everyone's favorite hero, and a real jerk
The Belgian Hare Jake's most hated nemesis!
The Gingerbread Man --- no spoilers, sorry
The MOOT - A very wise Moose with poor enunciation
Bulk Brogan - a semi-retired wrestler with a sad story... has it in for Jake