Ser Steffon Darklyn was one of the seven members of House Darklyn to be knights of the Kingsguard. Ser Harrold Darke was once his squire.
Ser Steffon was a member of the Kingsguard during the reign of King Viserys I Targaryen. He escaped King's Landing with Viserys' crown and joined Rhaenyra Targaryen on Dragonstone when her half-brother, Aegon II Targaryen, usurped the Iron Throne and began the civil war known as the Dance of the Dragons. He served as the first Lord Commander of Rhaenyra's Queensguard. When Prince Jacaerys Velaryon called for dragonriders, Steffon made an attempt but was burned to death by Seasmoke.