Jim Cummings became the voice of Winnie the Pooh in The New Adventures of Winnie the Pooh.
Cummings was chosen for the 1988 television series and went on to voice Pooh across many later Disney productions. His performance became one of the defining modern interpretations of the character.
Sterling Holloway was Disney’s original Pooh voice, beginning with Winnie the Pooh and the Honey Tree in 1966. Hal Smith later took over for several projects before Cummings assumed the role for the late-1980s television era.
Voice credits can vary by production, language and period, so a question about Pooh’s voice should identify the specific adaptation. For the 1988 animated series, the canonical answer is Jim Cummings.