Steven Spielberg is the executive producer of Freakazoid! (as well as Animaniacs, Pinky and the Brain and Tiny Toon Adventures). He is caricatured several times on the show. His voice is provided by Frank Welker.
Although he is generally shown to be involved in the process of scripting and producing Freakazoid! and Animaniacs, when Freakazoid, Wakko and the Brain show up at his conference room, Spielberg has no idea who they are.
At one point, he is directing a sequel to E.T.