Nielsen has provided voicework for several Norwegian dubs, and has dubbed many Disney characters, including Rex in Toy Story, Bernard in The Rescuers Down Under, P.T. Flea in A Bug's Life, Kaa in The Jungle Book (and sequels/spinoffs), Fillmore in the Cars movies, Merlin in The Sword in the Stone and the Mad Hatter in Alice in Wonderland. Non-Disney/Muppet credits include Plucky Duck in Tiny Toons and Snufkin in the Moomin series.