Hun-Apu and Ixbalanque decided to kill their father's murderers, as well as Zipacna, son of Vucub Caquix. They made a crab decoy and told Zipacna where he could find a giant crab to eat. When Zipacna went to the spot, they threw a mountain on him, killing him.
Hun-Apu became a sun god and his brother Ixbalanque became a moon goddess, switching genders.
Hunahpu and his brother were conceived in an unusual fashion, when their mother Blood Moon spoke with the decapitated head of their father Hun Hunahpu.
Hunahpu was immortalized as the Venus, the morning star, while Xbalanque became the full moon.
Xbalanque and his brother Hunahpu were quite inseperable in their lives, together outwitting arrogant gods and the lords of the Mayan underworld, Xibalba.
Although it is not explicitly stated in the Popol Vuh, Hunahpu seems to have been the dominant one among the brothers, often the one to do the talking and the planning, although Xbalanque was not merely a hapless sidekick.