Sir Dinadan was the son of Sir Brunor Senior, the 'Good Knight without Fear,' and brother of Sirs Brunor le Noir 'La Cote Mal Taile' and Daniel. He seems to have never had a wife or a lover. Dinadan had a very serious side to his character which led him to question the whole notion of courtly love. He saw no reason to try and kill some poor fellow knight over a misperceived insult, and thought hard about the righteousness of the cause and the chances of success before entering a fight. He was, however, a great practical joker, as particularly shown by his lampooning at the Sorelais Tournament.

Dinadan arrived at the jousting in disguise and performed brilliantly at the tilt. On the fifth day, King Galehaut sent Sir Lancelot to unhorse him and a bit of clowning on both sides led to Dinadan being unmasked. The next evening, Galehaut was in a fowl mood after being served fish, which he hated. Sir Dinadan then presented him with great headed fish with bulging eyes and quipped, "Well may I liken you to a wolf, for he will never eat fish, but flesh." The monarch then snapped out of his irritation and all laughed greatly. Again the following day, Lancelot continued the tom-foolery by entered the lists wearing a dress over his armour! He unhorsed Dinadan and, helped by a number of other pranksters, carried him into the forest and dressed him up like a woman too. Everyone was in hysterics, especially Queen Guinevere.

Sir Dinadan saw the good in everyone and had almost no enemies. Sir Tristram was his greatest friend. Unfortunately though, Sirs Mordred and Agravaine took a disliking to him, despite - or because of - his having rescued them both from Breuse Sans Pitie. He apparently also made some rather unfortunate comment concerning Sir Lamorak's death, causing the two to wickedly murder him during the Grail Quest. Sir Palomides brought him back to Camelot for burial.

His name is probably derived form the Welsh, Dynod.