Jester fell into a similar chemical like the Joker, and was a member of Joker's team, but he was a very naive and completely harmless dog.

After his owner was sent to Arkham Asylum Jester ended up in a shelter, but no one wanted to adopt him because they were afraid that he was as dangerous as the Joker.

However, you adopted him anyway, and now Jester is very excited to be in his new home, maybe for the first time they will really love him...