Given his appearance as elderly man as result of hi abuse of The Power, he may once bad, if not worse than Chase as both has abused their powers to the point of addiction. His abuse of power may caused the strain on his relationship with Caleb, but still love him nevertheless as he eventually willed his power for his son.
Reason why he wanted Caleb destroyed Chase was not only because Chase was the descendant of the traitor of the Covenant and also, prevent him to suffer the same fate with him.
Not much is known about him. He is a descendant of the Danvers family, most likely born in Ipswich. At some point in his early life, he fell in love with and married Evelyn, his wife, and had a son, Caleb. However, due to the great abuse of his powers, he aged a lot faster than he was supposed to, thus making him look like a 90-100-year-old man, when he was really just 44 years old. Since it would be impossible for him to make an appearance to the town without arising suspicions or even worse, expose the long-kept secret, he was presumed dead after a supposed accident and retired to the family's first colony house.
We first see a brief glimpse of him when Caleb goes there in order to deliver some medication to the butler that takes care of William, Gorman. Sarah was with him, but she never got in the house. She did, however, meet Caleb's father later on, when Caleb decided to reveal the secret of the family and the reason why Caleb had to get rid of Chase.
Later on, when Caleb goes to the Putnam barn to face Chase, Evelyn Danvers decides to visit her husband and plead him to will his powers to his son in order to fight Chase off. William finally gives in, thus giving away his life so his son could live on and defeat Chase.
- In the credits after the film, he's credited as "James Danvers" instead of "William Danvers".