• English / United States: Lucas
• Japanese / Japan: コウキ
• Japanese (Romanized) / Japan: Kōki
• Japanese (TL) / Japan: Koki

lucas-game is the male protagonist of the Sinnoh based Pokémon games (Diamond, Pearl, Platinum, Brilliant Diamond, Shining Pearl).

Game canon

If chosen by the player, Lucas leaves his hometown of Twinleaf Town, getting a starter from Professor Rowan, taking on Gyms, taking down Team Galactic, and becoming Sinnoh champion. If not chosen, he lives in Sandgem Town, and acts as Professor Rowan's assistant. Another character, rei-legends, strongly resembles him, and may be an ancestor or descendant of him, or neither at all.
Lucas appears in Pokémon Masters EX, where his sync pair is with Dialga. However, his starter is shown to be Chimchar in this canon, as he had Infernape beforehand.

Pokémon the Series

In the main series anime, he made a cameo battling against Brendan in Giratina and the Sky Warrior.

Pokémon Evolutions

He made a cameo in Pokemon Evolutions.

GOTCHA

He made a cameo in the anime music video "GOTCHA".