Complex sentence: While as an artist-illustrator living in The Bronx, New York, he first began his career in animation at the Raoul Barré cartoon studio in 1916, he joined the Fleischer Studio in 1923 where he developed the Koko clown character.
Split into simpler sentences: While as an artist-illustrator living in The Bronx, New York, he first began his career in animation at the Raoul Barré cartoon studio in 1916. He joined the Fleischer Studio in 1923 where he developed the Koko the Clown character.