Peaches was a gorilla owned by Haley's Circus.
Mad Hatter used Peaches to steal equipment for him. Though the gorilla brushed off Batman, Robin and Nightwing, Nightwing still recognized the gorilla. It put him on his path to Haley's Circus, where he found the Mad Hatter.
When Mad Hatter was almost defeated, he ran for Peaches' cage, hoping the gorilla could cover his escape. Nightwing destroyed the Hatter's hat, and Peaches took down Tetch herself.