From Bulbapedia, the community-driven Pokémon encyclopedia.
Diamond (Japanese: ダイヤモンド Diamond) is a character from Pocket Monsters DP who only appeared in PMDP10. He is from Twinleaf Town, Sinnoh. Diamond is based on Lucas from the Diamond and Pearl Versions games.
Diamond appears to be the celebrity type, people going up to him and taking pictures. He is well known around Sinnoh. He meets Red by greeting him a handshake. Diamond then shows off his Pokémon.