The Joker is a main antagonist of the Batman series. Although he does not appear in the Batman Beyond TV series, he appears in the animated film Batman Beyond: Return of The Joker as the main antagonist. He is voiced by Mark Hamill who also voices him in Batman: The Animated Series, The New Batman Adventures, and other Batman shows and games.
When The Joker showed up at Bruce Wayne's ceremony for his return to Wayne / Powers, Bruce and Terry McGinnis were so confused by how he was seemingly able to rise from the dead. It was soon revealed to Terry that Joker once captured Tim Drake and turned him into J.J. during this time, The Joker took state of the art technology and implanted a microchip with his DNA that would allow him to take over Tim's body at will, enabling to be "alive" in the future.