Eugene "Mercury" Morris, a fleet-footed running back for eight NFL seasons and a key cog in the undefeated 1972 Miami Dolphins, has died at the age of 77.

Morris teamed with backfield mates Larry Csonka and Jim Kiick as the Dolphins won back-to-back Super Bowls under coach Don Shula in 1972 and 1973.

Selected in the third round of the 1969 NFL draft out of West Texas A&M, Morris began his pro career as a kick returner, leading the NFL in kickoff return yardage as a rookie and taking one back 105 yards for a touchdown.

He became an effective change-of-pace back for the Dolphins, subbing in for the bruising Csonka, earning the first of three consecutive Pro Bowl honors in 1971.

Morris' best season came in Miami's perfect 1972 campaign. He rushed for an even 1,000 yards as he and Csonka became the first teammates in NFL history to run for 1,000 yards in the same season. He also led the league that year with 12 rushing touchdowns as the Dolphins capped a 17-0 season with a 14-7 victory over Washington in Super Bowl 7.

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Morris tallied 954 yards on an NFL-best 6.4 yards per carry in 1973 as he was again named a Pro Bowler and the Dolphins won a second consecutive Super Bowl.

He joined the San Diego Chargers for the final season of his career in 1976. He finished with 4,133 rushing yards and 35 total touchdowns – 31 rushing, one receiving and three on kickoff returns.

After retiring, Morris became one of the most prominent members of the undefeated Dolphins in their annual celebrations. He coined the term "Perfectville" to describe their unique place in history, and was perhaps the most vocal defender of their greatness in comparison to other dominant NFL teams that would follow.

"I played on the best team ever," Morris once told The Palm Beach Post. "We had some of the best players from 1971-74, we had the best record in history those four years.

"We ruled the football world.”