The Joker is the greatest of Batman's supervilains. He made 2 appearance
s in Scooby-Doo. He was voiced by Larry Storch

The Dynamic Scooby-Doo Affair

He teams up with Penguin as they are told by a mysterious hooded figure who told them to help "him" smuggle counterfeit money.

Caped Crusader Caper

Here he teams up with Penguin and kidnap a doctor which has invented a machine that can make you fly.

More info about Joker here : Joker on Wikipedia