Mascolo was best known in the recurring role of Stefano DiMera on "Days of Our Lives" from 1982 to 1985, returning briefly in 1988, again from 1993 to 2001, and making appearances again since 2007 until Stefano's death in 2016, making his final appearance on February 9, 2017, airing 2 months after his death, and won three Soap Opera Digest Awards. He has also played a wide range of roles on many different series including (but not limited to) a Stefano-like villain named Nicholas Van Buren on "General Hospital", and Carlos Alvarez on "Santa Barbara". Before achieving his fame, he was seen in the earlier soap operas "Where the Heart Is" and "From These Roots". He also made primetime television appearances on "All in the Family," "The Eddie Capra Mysteries", "Lou Grant" and "The Rockford Files".