Castor

Castor is the son of Dionysus and the twin of Pollux.

History
Castor is mentioned in The Lightning Thief by Percy. He notices that Dionysus only has two boys in his cabin, Castor and Pollux.

Castor fights bravely for the camp, and dies in The Battle of the Labyrinth by the hands of an enemy half-blood. His father Dionysus is depressed and angry over his son's death, surprising everyone by caring about his dead son.

At Castor's funeral, his twin brother Pollux tried to speak for his brother, but couldn't choke out the words due to his grief. He lit the funeral pyre, and walked away, trying not to cry.

It is most likely because of Castor's death that his twin Pollux survived the battle of New York City, as Dionysus requested that Percy keep him alive. Because of that request, after Pollux broke his arm, Percy asked him to stay out of battle as a personal favor.

Relationship with Pollux
It is shown that they were very close, and that they loved each other very much. Pollux was broken-hearted at his brother's death, and this helped his fury against Kronos and his monsters, so he had no doubts about him fighting for his brother's memory. They are always seen working together in the camp. Percy is also sad that he never really got to know Castor before he died as stated in The Battle of Labyrinth.

Abilities
Castor could control the states of the mind, and control grapes and strawberry plants, just like his father.