Riggilo is an adventurer who is found looting Durlag's Tower. See the Durlag's Tower Walkthrough for details.
He can be found on the third floor of the tower. If you kill the succubus, Kirinhale, you can give him a lock of her hair and he will give you a potion of cloud giant strength in return.
You may find it more lucrative to sell the lock of hair to the wizard at High Hedge for 250gp.