According to Wikipedia, Pierre Coffin voiced 899 Minions in Despicable Me 2. The figure refers to the production’s credited Minion voices, not to 899 separately famous characters with individual storylines.
Coffin was already central to the Minions before the sequel: he co-directed the first Despicable Me with Chris Renaud and helped establish the creatures’ distinctive vocal style. In Despicable Me 2, he again supplied the voices for the yellow henchmen, including recognizable characters such as Kevin, Stuart, and Bob.
The number is a useful reminder of how animation credits differ from live-action casting. One performer can record many variations of a character’s voice, with differences in pitch, rhythm, language-like sounds, and comic timing. Those recordings are then edited and assigned across large crowd scenes and individual gags.
Coffin’s role is sometimes confused with Chris Renaud’s. Renaud voiced some Minions in the first film, but the Wikipedia entry for Despicable Me 2 specifically attributes the 899-voice total to Coffin.