Queequeg was the callsign of one of Diamond Dogs' helicopter pilots. He was specifically responsible for ferrying Kazuhira Miller, Huey Emmerich, some Diamond Dogs soldiers, and (albeit unintentionally), Eli (the last of whom had stowed away in the storage container) to XOF's main base and Metal Gear Sahelanthropus's main hangar, OKB Zero.
After the XOF commander, Skull Face, had Venom Snake driven over to the real hangar for Sahelanthropus, Serak Power Plant, Queequeg tailed them and told Venom Snake that it was in position to provide cover, with Miller proceeding to tell him to get in a line of fire. Not long afterwards, however, its controls ended up malfunctioning, which was the result of Eli entering a symbiotic psychic link with Tretij Rebenok due to the former possessing a huge amount of hatred for Venom Snake, whom Eli believed to be his "father", Big Boss, which consequentially also resulted in Sahelanthropus's premature activation. After Sahelanthropus was defeated, Queequeg picked Snake up and returned to the ruins of the Serak Power Plant just in time to "see Skull Face", eventually leaving after Venom Snake, Miller, and Huey exacted revenge on him. It then returned to Mother Base's R&D Platform.
Behind the scenes
Queequeg follows the trend of Moby-Dick-based codenames in Metal Gear Solid V: The Phantom Pain (in this case, being named after the cannibalistic sailor). Other examples include Venom Snake and Big Boss being labeled "Ahab" and "Ishmael" while at the Dhekelia Memorial Hospital, and Venom Snake's chopper pilot being designated "Pequod." It was identified by name late into Main Mission 30: Skull Face, when it announced that it was in position.