Will's mother hated all things Gods. She joined a cult that's sole purpose was to limit God's powers and turn their children back to 'normal'. Zeus asked Apollo to go check it out and while Apollo was in disguise he fell in love with her and bore her only child- Will. He was spoiled as a child and was his mother's pride and joy. They got along great and she adored Will with all her heart. As he aged though she became suspicious and Apollo, watching over, became nervous that she'd learn Will's real identity. Will didn't learn how to read books like the other kids in his kindergarten class, but could read music after one lesson.
She eventually did a specialized blood test of Will and ran it anomalously through her cult's servers to protect Will's identity. Apollo snatched Will away when the results came back that he was half God. Apollo sent Will to Camp Half-Blood with the promise that once a year they would do something together since he never had a parental figure. This left Will with serious trust issues and a fear of Doctors and needles.
Will's excelled at bow and arrow and quickly rose to the top of his cabin. After the titan war he was given the Head Counselor position as well as becoming a renowned healer. He had healed Annabeth after she took the dagger for Percy during the war.