Question: In which year, did this earliest guest star in 1999 for SpongeBob SquarePants stop providing the voice?
Sentence (from "List of SpongeBob SquarePants guest stars"): He began developing "SpongeBob SquarePants" into a television series in 1996 upon the cancellation of "Rocko's Modern Life", which Hillenburg directed.
Relevant evidence: No