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

Llewelyn ap Gruffydd is the Prince of Wales. Under Welsh law, the kingdom is divided and split between the sons in a succession in contrast to English law, which grants the succession to the oldest son. Sharing Wales is not easy for Gruffydd's sons, and they go to war with each other. Owain, the eldest son, is imprisoned by his brother Llewelyn and locked away in Dolbadarn Castle. Davydd is Llewelyn's favorite brother. Twice Davydd has rebelled, but he has been forgiven. The youngest brother Rhodri rebels with Davydd and Owain, but his lands are confiscated and he is forced to leave Wales.