Sir Gaheris was the son of King Lot of Orkney and his wife Morgause, sister of King Arthur, before being knighted he was squire to his elder brother Gawaine. Sir Gaheris married Lynette on the day his brother Gareth married hersister, Dame Lionesse, of the Castle Perilous.
The two brothers were slain in the struggle following the rescue of Queen Guinevere from the fire, though this was by accident as Sir Lancelot did not recognise them in the crowd. Sir Gawaine for a long time held Sir Lancelot in bitter hatred.
Gaheris, like his other brothers, first visited Arthur's court when Morgawse arrived following the Battle of Bedegraine. When Gawaine returned to be made a knight at Arthur's wedding to Guinevere, Gaheris was by his side to act as his page. In a way, he acted as Gawaine's conscience, cooling his hot temper when Gawaine wished to challenge Pellinore, praising him for his skills in his combat with Allardin of the Isles, and admonishing him after his failure to show mercy causes the death of the lady of Ablamar of the Marsh.
But throughout Gawaine's early adventures, Gaheris was his steadfast companion. There were two Gaherises that were Knights of the Round Table. This one was the brother of Gawain, Gareth, and Agravain.