Greg Mac Lochlainn is a phone caller from Five Nights at Treasure Island. He talks on Night 1, and is very friendly towards the player. It is very likely that he is in charge, or a higher-up, of the research team, as he mentions legal issues in his call. He also mentions that there are what they thought were suits, but aren't (specifically a photo-negative suit in older versions, referring too them as suits and nothing else), and tells the player that the toons can't see, but have good hearing. Shortly, after, he says, "Now, I'm sure you've heard the rumors floating around the workplace, and legally, I can neither confirm or deny any suspicious activity due to a... supernatural being", further suggesting that he is the leader of the research team. He then goes on to explain the main game mechanics of Five Nights at Treasure Island and hints towards Henry before ending his call.
Greg's phone call is the longest of the available phone calls.
Greg's full name was confirmed to be Greg Mac Lochlainn in TGsEE.