"It is with great sadness we announce the passing of Oilers legend Dave Semenko after a short, but courageous battle with cancer," the Oilers said in a statement. "Dave will be remembered as a fierce competitor, loyal teammate, fan favorite and dear friend to so many. His legendary toughness on the ice is surpassed only by his kindness and caring for others, and his equally legendary wit and sense of humor. Our hearts go out to Dave's family and many friends."
Kevin Lowe, vice chairman of Oilers Entertainment Group, said the banners hanging in Rogers Place honoring Edmonton's all-time greats were indicative of Semenko's influence and guidance.
"I think it's safe to say without overstating anything that the greatest of all time who [have banners] up in the building at Rogers, as [Paul Coffey] alluded to, those greats couldn't have done without the support and aid of Dave Semenko."
Semenko, a Winnipeg native, joined the Oilers for the 1977-78 World Hockey Association season. He scored the last goal in the history of the WHA, in a 7-3 loss to the Winnipeg Jets in Game 6 of the Avco Cup Final, and then moved with the Oilers to the NHL for 1979-80, playing with Edmonton until he was traded to the Hartford Whalers on Dec. 12, 1986.
He played 51 games for the Whalers in 1986-87 and 70 for the Toronto Maple Leafs the next season.
"One of the first Oilers I met in 1978, I didn't know at the time the impact he would have in my life and my career," Gretzky said in a statement. "He was the toughest player I knew and yet the biggest teddy bear you would ever know. A beloved Oiler that will be missed dearly because of his kind heart and funny sense of humor. He made us all better people."
"The news of Dave passing this morning literally took my breath away," Hockey Hall of Famer Mark Messier said in a statement. "I loved [Semenko] like we all did. He was a great teammate, a loyal friend, a loving father and a worthy champion."
Semenko finished his career with 153 points (65 goals, 88 assists) and 1,175 penalty minutes in 575 NHL games.
His former teammates detailed his considerable contributions to the Oilers. His on-ice presence and authority was especially vital for a young team on the verge of greatness.
"Would the Oilers have won their first two Stanley Cups (1984, 1985) without Dave Semenko?" Marty McSorley said in a phone interview with NHL.com. "It would have been a much harder task. There were these 21-year-old kids that were flying around the ice and a little cocky -- in a good way.
"In beating the Philadelphia Flyers and the New York Islanders, these were tough teams. His presence was huge. He had a tremendous sense of humor. You had to listen to him because he would say things and it would float by."
Coffey echoed those sentiments at a news conference in Edmonton with Lowe and Charlie Huddy.
"Dave was the guy that made it fun," Coffey said. "He made it safe to go out and play with the big guys, going to Philadelphia, going to the Islanders, playing against the tough teams, and allowed myself and all the skilled players on that team to do what they did best. He was great at it."
The Oilers said Semenko was first diagnosed with cancer three to four weeks ago, after he called former Oilers head medical trainer Kenny Lowe, the brother of Kevin.
"I guess he had not been well for a couple of weeks," Kevin Lowe said. "There was no record of any of his recent health, because he hadn't been to a doctor in 15 years because I guess he had been the picture of health.
"The prognosis had been not great, but it felt treatable at the time, and it was just a rapid descent."
Coffey said that Semenko's wit and candor were with him until the end.
"It was a tough day for us all," Coffey said. "We all found out about a month ago, and I had the pleasure of being with Dave and playing with Dave and there wasn't a fight he didn't win. Unfortunately, this wasn't his fight to win. It's a terrible disease and he's the biggest guy I've seen taken down that fast, and that was sad. He did it with dignity. He was surrounded by his daughter and his friends."
Huddy, an assistant coach with the Jets, had been working this week at Winnipeg's development camp and made his way to Edmonton to try to see Semenko.
"The guys called me last night and told me [Semenko] wasn't doing good, and unfortunately I didn't get here in time," Huddy said. "… The stories go on and on about [Semenko] and how good of a teammate he was and made all of us safer on the ice. I don't think I saw him lose any fights. There was some tough guys back then, and he wasn't backing down."
After retiring in 1988, Semenko joined Oilers radio broadcasts as color commentator, and then was an assistant with Edmonton during the 1996-97 season. He was a pro scout for the Oilers from 1997-2015.
Lowe said there will be a memorial service for Semenko next week.
"I'm devastated," Lowe said. "He loved what he did, this was the first year he wasn't scouting but was an ambassador. He was the first-ever Oilers ambassador. We had so many comments from our customers and our employees of how fortunate they were to be able to work with him.
"And he was so happy, so happy of not traveling and he was really happy with the new building, the team and what he was doing, and he was really looking forward to the coming years. I'm shocked that this all went down so quick, and I'm going to really miss him."
NHL.com correspondent Derek Van Diest contributed to this story.