Big Top is a hulking criminal who works for the Circus of Strange.
After Mister Toad was apprehended by the Gotham City Police Department. Big Top and a couple more members of the Circus of Strange were dispatched to seemingly rescue Toad. Big Top was maimed by the new Robin and arrested by the Gotham City Police Department.
In the New 52, Big Top briefly appeared in the first issue of the Court of Owls storyline where he was shown to be an inmate of Arkham Asylum.