Williams, who had recently undergone a kidney transplant, died Sunday while taking a walk near his home, the Minneapolis Star Tribune reported. The Hennepin County medical examiner's office confirmed his death.
Born in Jackson, Miss., on Oct. 27, 1945, John McKay Williams was a high school football star in Toledo, Ohio. A three-year letterman at the University of Minnesota, he was an All-America and All-Big Ten offensive lineman in 1967, when the Gophers went 8-2 and won a share of the conference title.
In the 1968 NFL draft, the Baltimore Colts picked him in the first round, 23rd overall. He played four seasons with the Colts and went to two Super Bowls, winning a ring with the team's 16-13 victory over Dallas after the 1970 season.
Williams was traded to the Rams for a No. 1 pick in 1972 and started at right offensive tackle for six years. He played guard in 1979, when the Rams advanced to the Super Bowl, losing to the Pittsburgh Steelers, 31-19, in January 1980.
By then Williams had a plan for his post-football life. He had earned a bachelor's degree in education from Minnesota but really wanted to be a dentist, so he began taking classes at the University of Maryland at Baltimore.
"I knew I was doing the right thing when I couldn't get a decent off-season job in 1970 after playing on Baltimore's Super Bowl team," he told The Times in 1978.
It took him five years as a part-time student before he earned his doctorate in dentistry. He retired from the NFL after tearing a calf muscle during the 1979 season and moved back to Minneapolis to open his dental office.
The 6-foot, 3-inch 256-pounder described his off-the-field work with patients in the Times interview.
"There is curiosity and some of that normal fan-athlete identification," he said. "But the main thing is rapport. Rapport is everything in dentistry. The ability to instill confidence."
In Minneapolis, Williams worked to revitalize the urban district where he established his business and was named the city's volunteer of the year in 1992.
Trained in forensic dentistry, Williams joined a team of public health professionals who helped identify remains of victims after the 9/11 terrorist attacks.
"A horrific experience," Williams told the Minneapolis Star Tribune in 2002.
In 1983, Williams pleaded guilty to selling cocaine. He cooperated with authorities' investigations into related cases and served seven months of a five-year sentence in federal prison.
"When I'm asked about it, I always tell people," Williams said in the Star Tribune interview. "I don't deny it. It's something that happened, and I wish it wouldn't have. But I also think I'm a better person for it."
Survivors include his wife, Barbara Butts Williams, and children from a previous marriage that ended in divorce.