Casting HBO's Justice League Dark

Detective Chimp was not a member of the original Justice League Dark, but subsequently became one in the version created under DC's New Justice banner.

Upon his introduction in the 2018 series, the character is bitter and a drunk. He saw a lot of friends die during Dark Nights: Metal and has been entrusted with a responsibility he did not want, hence those aforementioned qualities.

These are qualities that were perfectly reflected by Tom Hollander in The Night Manager, a role that actually won him the BAFTA for best supporting actor. Get Hollander to channel that performance for Detective Chimp and DC has an excellent representation of the character as he was presented in the Justice League Dark books.