William "Willie" Francis Tanner is the father of the Tanner family, performed by Max Wright, and a social worker at the Social Services Department of Los Angeles County. Willie is a shortwave radio enthusiast, and it was a result of his shortwave radio signals that ALF followed them and crashed into his home. Willie also avidly collects scale model train sets. He was born in Decatur, Illinois, (although he claims to be from Ohio when the support group comes to the Tanner house) and he attended Claremont High School, then later graduated from UCLA. Willie also claims to have gone to Amherst College. Willie has a bachelor's and master's, although it is unknown which degree was attained from which school. Willie majored in social science. When Willie uses his homemade ham radio to call somebody, he uses the callsign "K726 XAA".
He was arrested by the FBI after ALF made radio calls to Air Force One, but after another call came in while Willie was in custody, his innocence was determined as he could not have been two places at once, and Willie was released by the President. Like his wife, Kate, he was a flower child during the 1960s.
Willie's mother wore a wig, something that made Willie sad to discover when he was six years old. Willie had a grandfather that taught him to walk away from his bully Clarence instead of trying to fight him. The same grandfather apparently talked to corn chips.
Willie has had a somewhat difficult relationship with ALF. He does not appreciate ALF's carelessness or party animal attitude. Sometimes, what ALF would do what would cause Willie to lose his temper and get very angry with him, often followed by Willie screaming loud or banishing ALF to the garage. As Willie has been interested in astronomy, he considers it a blessing that ALF has landed in the Tanner home and is genuinely interested in what Melmac was like.
- Parents: Unnamed Parents
- Brother: Neal Tanner
- Wife: Kate Tanner
- Daughter: Lynn Tanner
- Son: Brian Tanner
- Son: Eric William Tanner
- Mother-in-law: Dorothy Halligan Deaver
- Father-in-law: Sparky (decsased)
- Stepfather-in-law: Whizzer Deaver
- Sister-in-law: Unnamed Sister-in-law
- Great-Grandfather: Silas Tanner (decsased)
- Uncle: Uncle Albert (decsased)
- Uncle: Doug (decsased)
- Aunt: Pat
- He speaks to ALF more frequently than the rest of the Tanner family.