Who is Owain ap Gruffydd from The Reckoning and what is their importance?

Owain ap Gruffydd is the older brother of Llewelyn ap Gruffydd. Unsatisfied with his inheritance, he leads his younger brothers, Davydd and Rhodri, in a rebellion against Llewelyn. The rebellion fails and Owain is imprisoned by Llewelyn. Owain spends years imprisoned in Dolbadarn Castle, released as an old man as terms of Llewelyn's surrender after the second war between Wales and England. Owain is treated well as a royal prisoner, a testimony to Llewelyn's fairness and in contrast to most political prisoners of King Edward.