After acquiring the Relics (except for the Greaves and the Sword of the Crusader), Lathon will arrive at the Priory of the Nine to give the Hero the Greaves. He will explain that Sir Roderic had discovered the resting place of Sir Berich, who took the greaves and the Sword of the Crusader with him to war. When they arrived they were attacked by Berich's Wraith, now known as Lord Vlindrel. Sir Roderic sent Lathon away with the greaves while he held off the wraith.
After finishing the Knights of the Nine questline, Sir Lathon can be recruited as a follower, but it is possible for him to be killed while accompanying them. If this occurs, he will be replaced by a Knight of the Nine.