From A Wiki of Ice and Fire
|Book(s)|| A Game of Thrones (Appears)|
A Clash of Kings (Appears)
A Storm of Swords (Mentioned)
A Feast for Crows (Mentioned)
A Dance with Dragons (Mentioned)
A Game of Thrones
Robb Stark takes Olyvar as a squire as part of the pact sealed between Catelyn Stark and Lord Walder to join the Freys to the Stark cause in the War of the Five Kings. Two years older than Robb, Olyvar is considered an excellent squire who proves his devotion to Robb and the Starks. He fights by Robb's side in the Battle of the Whispering Wood.
A Clash of Kings
A Storm of Swords
When the Freys abandon Robb's cause due to his marriage to Jeyne Westerling, Olyvar wishes to stay with him, but the other members of his family force him to ultimately return. He does not participate in the Red Wedding, and Ryman Frey claims that Olyvar could not attend because he was "on duty." It is possible that the other Freys kept him away due to his friendship with Robb. No information has yet come to light about his reaction to the Red Wedding or his actions afterwards.