Ser Gwayne Gaunt is an unseen character in Game of Thrones. He is not expected to appear in the series, being long dead by the time it starts. Ser Gwayne Gaunt was a knight of House Gaunt and sworn brother of the Kingsguard of Aerys II Targaryen.
In the books
In the A Song of Ice and Fire novels, little is known of Ser Gwayne Gaunt, except that he died during the Defiance of Duskendale where he was killed by Ser Symon Hollard. Ser Barristan Selmy avenged his death.