Lucas (Japanese: コウキ Kōki) is the male player character of Pokémon Diamond and Pearl. The female counterpart is Dawn. If the player chooses Dawn, he will become Rowan's assistant for the game. Lucas lives in Sandgem Town with his little sister, grandfather, and father - who works as an assistant of Professor Rowan. He is already the Professor's assistant at the beginning of the game. He also demonstrates to the player how to capture Pokémon by capturing a wild Bidoof.
The character Diamond from the Pokémon Special manga is based off of the design of Lucas.
His English name is derived from "lux", the Latin root word for light, while his Japanese name is a reference to the Japanese word for "brightness" (光輝 kōki), much like Hikari means light (光). It is also similar to 金剛石 kongōseki, a Japanese word for diamond.