Lucious is a younger brother of Celie and Nettie. In Celie's second letter, she says that Alfonso (the man she believes is her natural father but is really her stepfather) was trying to get her mother to sleep with him very soon after Lucious was born, and Celie herself is just fourteen years old at the time. It was shortly after this — because her mother refuses him sex — that he begins to rape Celie. The only other time this child is mentioned is when Mr. comes to inquire about marrying Nettie and Alfonso will only let him "have" Celie. Celie says:
I turn round. One of my little brothers come up. I think it was Lucious. He fat and playful, all the time munching on something. He say. What you doing that for? Pa say. Your sister thinking bout marriage.
Lucious is too young to really understand what that means, and he doesn't seem to care anyway. He just asks Celie if he can have some blackberry jam, and she tells him that he can. Alfonso uses this as a selling point: he tells Mr. that Celie is good with children, as Mr. has several who need cared for.