It has been 33 years since Donnie Shell announced his retirement and almost two decades since any of his teammates from the 1970s were inducted into the Pro Football Hall of Fame. On Wednesday, after an excruciatingly long wait, Shell became the 10th player from the Steelers’ four Super Bowl teams of the 1970s to make the Hall of Fame.

Shell made it as part of the Centennial Class in celebration of the NFL’s 100 anniversary. He joins defensive teammates Mel Bount, Jack Ham, Jack Lambert, Joe Greene and offensive teammates Terry Bradshaw, Franco Harris, John Stallworth, Lynn Swann and Mike Webster in the Hall of Fame. Amazingly, Shell, Lambert, Stallworth, Swann and Webster all arrived in 1974 as part of the best rookie class in the history of professional football.

All of Shell’s Hall of Fame teammates entered the NFL with some pedigree, but he did not. He was an undrafted free agent out of South Carolina State, a historically black college that did not send many players into professional football. Discovered by Bill Nunn, the legendary Steelers scout, Shell had to earn his spot on the team through the grunt work of special teams.

“His nickname was ‘The Torpedo’ because of the work he did on special teams,” said Ham, who played for the Steelers from 1971-82 and was enshrined in the Pro Football Hall of Fame in 1988. “He made a name for himself on kickoff and punt coverage. He worked his way up. He reminded me of Rocky Bleier in that way. He continued to work hard, and to his credit, he became a Hall of Fame safety.”

Shell was a backup safety and special-teams player on the Steelers’ first two Super Bowl teams in 1974 and ’75. He did not become a full-time starter until the 1977 season — and under some very unusual circumstances. He replaced Glen Edwards, who was selected first-team All-Pro after the ’76 season.

“After the 1976 season, all four of our defensive backs made the Pro Bowl,” former Steelers safety Mike Wagner said. “It was J.T. Thomas, Mel Blount, Glen Edwards and me. So the coaches come up to me and tell me they want to move me from strong to weak safety. They felt like Donnie was ready to play. Well, I thought that was curious because Glen was an All-Pro. But we had all been around Donnie. We knew he could cover, and he was a great hitter.”

It turned out the coaches knew what they were doing. Shell had three interceptions and a fumble recovery during the ’77 season. Edwards became a starter again when Wagner injured his neck and had to miss the remainder of the season. The following season, the Steelers traded Edwards to the San Diego Chargers.

Shell, meanwhile, made his presence felt on the final two Super Bowl teams of the ‘70s. He might best be remembered for a crushing hit he delivered on Houston running back Earl Campbell late in the ’78 season. The AFC Central division title was on the line in the Astrodome, and Shell fractured Campbell’s ribs with a tackle that knocked him out of the game. The Steelers won, 13-3, and went on to beat the Oilers in the AFC title game at Three Rivers Stadium en route to their third Super Bowl win.

“If you look at the play, it was an off-tackle run, and two of our great players, Jack Ham and L.C. Greenwood, get kind of driven back,” Wagner said. “I come up to fill the hole, and Earl spun. It looked like he was going to run to daylight. Then, all of a sudden, Donnie drilled him. That was probably the key play for him in his career.”

“His physical play is something that stood out,” Ham added. “He was a hybrid linebacker/defensive back. He brought a physical presence to those great defenses we had.”

Shell joins a short list of undrafted players to make the Pro Football Hall of Fame. He is just the 17th player who entered the league as a free agent to be inducted. The most recent before Shell was former Minnesota defensive tackle John Randle, who was enshrined in 2010.

Shell retired in 1987. He is third on the franchise’s all-time interceptions list with 51. Only Blount and Jack Butler, another Hall of Famer, have more. Shell also had 19 fumble recoveries and scored four touchdowns in his 14-year career.

This year’s Hall of Fame class includes 20 members — 10 players from 25 seasons ago or longer, three contributors and two coaches along with the five modern-day candidates that will be selected by the writers in the traditional process the day before the Super Bowl next month.

The 15 Hall of Famers from bygone eras were chosen by a blue-ribbon panel comprised of Hall of Famers, coaches, executives, historians and Hall of Fame selectors. The 20 for ’20 class is being done in conjunction with the NFL’s 100 anniversary.

In addition to Shell and the previously announced elections of coaches Bill Cowher and Jimmy Johnson, the others announced Wednesday include: Steve Sabol, George Young, Paul Tagliabue, Harold Carmichael, Jimbo Covert, Cliff Harris, Bobby Dillon, Winston Hill, Alex Karras, Duke Slater, Mac Speedie and Ed Sprinkle.

It’s shaping up as quite the summer for the Steelers in Canton. Cowher and Shell could be joined by Troy Polamalu and Alan Faneca, who are among the finalists this year as modern-day candidates. Polamalu is in his first year of eligibility. Faneca has been among the finalists for the past several years.