Edwards said Christensen battled liver disease and various other related illnesses for about two years. Longtime BYU football secretary Shirley Johnson, now retired, said doctors recently found what was supposed to be a "perfect match" for a liver transplant, but the operation was not successful.
"Todd had a great spirit about him and was a true friend. I feel so blessed to have been around him so much," said James Bates, Christensen's broadcast partner on the MountainWest Sports Network, a position Christensen held until the Mtn. shut down in 2012.
Christensen, a devout Mormon, did not drink alcohol. His son, former BYU receiver Toby Christensen, told The Associated Press that his liver problems started 25 years ago after a "botched" gall bladder operation.
Reminiscing, Edwards said Christensen often would appear distracted when coaches were talking to him at practice and would "stare at the mountains or off into space somewhere," but he picked up things more quickly than any other player.
"Todd came in and started for us for four years, and he grasped our offense and what we did more quickly than any player I can remember," Edwards said. "Our offense was not easy to pick up because a lot of it depended on the way the defense was aligned. But Todd got it all right away, even as a freshman."
After playing running back at BYU from 1974 to 1977, Christensen was the Dallas Cowboys' second-round pick in the 1978 NFL Draft. He was cut by the Cowboys after breaking his foot before landing with the Raiders. He played in Oakland for 10 seasons at tight end and won Super Bowls in 1981 and 1984.
"Definitely one of the all-time greats," former BYU quarterback Robbie Bosco said. "He will always be remembered."
At BYU, he caught 152 passes for 1,568 yards and 15 touchdowns mostly from Marc Wilson and Gifford Nielsen and was an all-Western Athletic Conference pick in 1977. He was inducted into the BYU Athletics Hall of Fame in 1992.
His NFL career took off in 1982 when he caught 42 passes for 510 yards and four touchdowns in a strike-shortened season. In 1983, his best season in the pros, Christensen caught 92 passes, an NFL record for tight ends at the time, for 1,247 yards and 12 touchdowns.
Religious, thoughtful and the son of a professor, Christensen didn't fit the Raiders mold, but he once told Edwards he liked playing for the franchise because it was more accepting of "odd personalities" than any team in pro sports. He authored three books of poetry, for example, and would use large, polysyllabic words in everyday life and broadcasting.
"Todd represented BYU in a way that you would want all your former players to represent your school," Edwards said. "He was his own person, but he got along with people of all walks of life really well. That was one of his strengths."
After retiring from football, Christensen worked as a color commentator for NBC Sports from 1990 to 1994. He also did commentary for ESPN and the Mtn. He called Navy games for the CBS Sports Network in 2012.
Christensen was born in Pennsylvania but grew up in Eugene, Ore. and starred at Sheldon High in football and track. He was inducted into the Oregon Sports Hall of Fame in 2000.
He is survived by his wife, Kathy, and four sons. Funeral arrangements are pending.