Claus is the son of Flint and Hinawa and the brother of Lucas in Mother 3. Claus resembles his brother Lucas in all features except for his hair, which is orange instead of blonde. His name is an anagram of Lucas and vice versa.
Claus is actually a more important character than what the beginning of the game reveals. Claus makes a brief appearance at the beginning of the game in Chapter 1. After his failure to avenge his mother's death at the hands of Mecha Draco, the boss at the end of Chapter 1, it is assumed by his still body found at the bottom of the cliff that he too has died. However, near the end of the very last Chapter, Chapter 8, it is found out that Claus is actually The Masked Boy introduced at the end of Chapter 5. Pokey reveals near the end of the game, before you fight him, that he had Claus converted into his loyal robot toy to use as his key to remove the 7 needles that sealed away the dragon sleeping under Nowhere Islands so he could use it to conquer the world. At the very end of the game when brainwashed, Claus tries to kill Lucas. However, Hinawa, who dies near the end of Chapter 1, appears as a voice to Claus and tells him to stop attacking Lucas. Claus then takes off his suit and appears as himself one last time before his brother before he dies.