John Howlett was the stepfather of Wolverine.
John Howlett was caring for his son James before he was shot dead by his groundskeeper, Thomas Logan (who was also having an affair with John Howlett's wife). His death is what triggered James' latent mutation, which James soon used to kill Thomas, avenging John.
Before dying, Logan revealed that it was not John who was James' father, but he (Logan) himself. Soon after, James and Logan's son Victor Creed (who is revealed to be James' half-brother) and who has a similar mutation to James, run away and eventually become soldiers in the U.S. military for the next 120 years due to their healing factors.