Luke is the younger brother of Garian.
Parallel I[]
Garian mentions Luke to Jack in Parallel I, informing him he had not seen Luke in while.
Parallel II[]
In Parallel II, it is revealed that Bilan captured Luke. After Bilan is defeated by Garian in the Captain's Cabin, Luke is freed but is dying. Garian remembers that the Diary of Wouda mentions a cure, and travels to Jailer's Island to find it in order to find a cure for Luke.