Agravain was an assassin employed by Morgan le Fay to serve as one of the knights. Acting as the secretary of the Round Table, he was one of the few to find out the secret of the King's gender. The affair between Lancelot and Guinevere was discovered by him, and he used the secret of the king to threaten the queen.
Serving on the Round Table, Agravain often advocated more so than the others of the King's inhuman nature. He often pronounced to the other knights that, "The King is not the incarnation of the dragon; his heart is a single dragon. His magical power is of a level beyond ours. I ask you not to seek the same values as ours from one possessing magic like the gods."
He is calm, calculated and even cruel, always going for the best option at hand. He believes his purpose is to assist the appropriate King of Britain, thus despite Morgan's order, he claimed that he helped Artoria willingly, believing her to be the best king Britain could have. He however hates women due to Morgan, and was shocked to discover Artoria's gender when exposing Guinevere's affair.
When he is about to die, however, he confesses his real wish was to build a perfect kingdom for his king. It wasn't that he served the king for the kingdom, but the kingdom for his king. The only person he doesn't want to be hated by.
Although he rarely fought on the front lines, he gained the moniker "Agravain who knew no wounds" because would always return uninjured whenever he went to battle, no matter the strength of the opponent. He is a very capable fighter, defeating and killing even Lancelot who was summoned as a Saber, but only after drugging himself and boosting his capabilities, and is left mortally wounded afterwards.
As part of the Round Table, his attitude earns him general dislike, but no doubt excels as the king's secretary. Bedivere notes that Camelot's fall accelerates only after his death, and he may be the most important person holding the Table together.