The late Sjef Poort performed the voice of Forgetful Jones ("Vergeetachtige Jan") on Sesamstraat, the Dutch co-production of Sesame Street.

Poort was mostly active during the 80s, and performed voices until the mid-90s. For a long time, he was one of the main singers. He also performed the voices of Hard Head Henry Harris, Harvey Kneeslapper and Oscar the Grouch in the song "Swamp Mushy Muddy" (one of the only Oscar appearances of that era).