Nathan Drake's older brother introduced in Uncharted 4 is Sam Drake. His full name is Samuel Drake, and he is voiced by Troy Baker in the game.
Sam was presumed dead after a prison escape went wrong years before the events of A Thief's End. He reappears and claims that drug lord Hector Alcázar forced him to find Henry Avery's lost pirate treasure. This revelation pulls Nathan out of retirement and begins the game's central adventure.
Sam and Nathan's relationship drives much of the story. They share a history of exploring, deception, and rivalry, while Sam's apparent desperation repeatedly puts Nathan and Elena at risk. Players also see a younger version of Sam during flashback sequences.
Sam is sometimes confused with Victor Sullivan, Nathan's longtime mentor, or Rafe Adler, the game's principal human rival. Neither is related to Nathan; Sam is specifically his older brother.