Mascolo passed away Wednesday, but NBCUniversal announced his death Friday.
He joined the daytime drama in 1982 and was featured intermittently until his last appearance this year.
"Joseph was a big 'ol bear with a puppy dog heart. I'm so blessed to have had these many years with him. I will miss him every day," said his wife, Patricia Schultz-Mascolo
, according to The Hollywood Reporter.
Mascolo had many roles in a decades-long acting career but was best known as DiMera, a villain also known as "The Phoenix" for many dramatic comebacks from supposed demise. He won three Soap Opera Digest awards for outstanding villain.
He last appeared on the show in January, when his character apparently was shot to death. Naturally fans wondered whether "The Phoenix" would rise again, but Mascolo hinted otherwise.
"Last spring, I had a small stroke," he told Soap Opera Digest in January
. "During my rehab, I thought this would be a good time for Stefano to leave.
"The producers visited me and we worked out a tentative plan, and the writers beefed up the storyline to what you see on TV."
News of his death spread on social media, and fellow co-stars and fans expressed their condolences.
"It won't be the same," tweeted Thaao Penghlis, an actor who has played the characters Andre and Tony DiMera on "Days."
"So long Joe. I'll miss you, yet a part of you will always be with me and for that beautiful gift I am so happy and grateful" posted James Scott, who played Stefano's son EJ DiMera on the soap.
Eileen Davidson, who portrayed Kristen DiMera, tweeted: "Very sad to hear of the passing of the great Joe Mascolo. God bless him and keep him."
"Just like sand through the hour glass so are the days of our lives. #JosephMascolo RIP," posted a fan.
Musician turned actor
Born and raised in West Hartford, Connecticut, Mascolo didn't initially have acting in mind. In college he studied classical music and had dreams of becoming a conductor, according to his official website
. A drama coach overhead his booming basso voice and encouraged him to explore acting.
His acting career began when he joined an off-Broadway production of "The Threepenny Opera."
Becoming a daytime drama villain
Mascolo appeared in a wide-range of television shows, including "All in the Family" and "The Gangster Chronicles," before moving to daytime drama.
"Days" wasn't Mascolo's only soap. He had a brief role on "General Hospital" in 1989 and a recurring role in "The Bold and the Beautiful" from 2001 to 2006.
Mascolo is survived by his wife, his son, stepdaughter, five grandchildren and three great-grandchildren.