This is the one crossover to rule them all.

Actor Andy Serkis is the master of motion capture acting, bringing characters to life like no one else can. When Serkis stopped by “Conan” to promote his new movie, “Dawn of the Planet of the Apes,” host Conan O’Brien asked him what would happen if two of his most famous characters, Gollum from “Lord of the Rings” and Caesar the Ape, had a phone conversation.

The answer: dreams come true.

“Conan” airs weeknights at 11:00 p.m. ET on TBS.