Marvin Miller, who turned the Major League Baseball Players Association into one of the most powerful unions in the United States, and Ted Simmons, a hard-hitting catcher whose stellar career was overshadowed because he played at the same time as Johnny Bench, were elected Sunday to the National Baseball Hall of Fame.

Miller, who died in 2012 at age 95, negotiated the sport's first collective bargaining agreement, won players' freedom from the reserve clause that effectively tied them to their teams for life and helped to usher in the era of free agency that saw major-league players' average salary rise from $19,000 in 1966 to $326,000 when he retired in 1982.

He presided over major strikes in 1972 and 1981 to force team owners to pay players what he thought they were worth. During the most recent baseball season, the average player's salary was $4.36 million.

Miller was widely despised by baseball's owners and corporate administrators, no more so than by Bowie Kuhn, the longtime commissioner of baseball who was inducted into the hall nine months after he died in 2007, one of the many years Miller was overlooked.

Miller, who was lead economist and negotiator for the United Steelworkers union when he moved to the players association in 1966, was widely perceived to have bested Kuhn many times in negotiations.

But players and those close to them saw Miller as a transformative figure.

Henry Aaron, who held the career record for home runs when he retired from baseball, was once quoted as saying: "Marvin Miller is as important to the history of baseball as Jackie Robinson."

The legendary announcer Red Barber agreed, saying in a 1992 Village Voice profile: "Marvin Miller, along with Babe Ruth and Jackie Robinson, is one of the two or three most important men in baseball history."

Retired players had campaigned for almost two decades to get Miller into the Hall of Fame, He failed to win election in 2003, 2007, 2008, 2010, 2011, 2014 and last year. When he was finally elected Sunday, it was by the hall's Modern Era Committee, which assesses the cases of baseball figures overlooked in the main annual balloting.

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Curt Flood Jr., the son of Curt Flood, the St. Louis Cardinals outfielder whose challenge to the reserve clause laid the groundwork for the union's campaign for free agency, tweeted Sunday: "Marvin Miller belongs in the National Baseball Hall of Fame and Museum. Period."

Simmons, 70, was a highly admired switch-hitting catcher with 248 home runs and almost 2,500 hits in a 21-year career from 1968 to 1988, primarily with the Cardinals but also with the Milwaukee Brewers and the Atlanta Braves.

But Simmons was eclipsed during the 1970s by Bench, the Cincinnati Reds catcher whom many have called the greatest catcher of all time. Simmons hit for higher averages — .301 during the 1970s, compared to Bench's .269 — but Bench was a better power hitter, having hit exactly 100 more home runs during the decade than Simmons' 169.

Bench was also considered a much better defensive catcher. He won 10 straight Gold Gloves as the best defensive catcher in the National League from 1968 to 1977; Simmons never won the award.

But Simmons remains a career leader among catchers in many batting categories. An eight-time All-Star, he hit .300 or better seven times, including three straight seasons beginning in 1971.

He was honored with the Silver Slugger Award as the best-hitting catcher in the National League with the Cardinals in 1980, and he caught no-hit games pitched by Bob Gibson in 1971 and Bob Forsch in 1978.

Bench, himself, said Sunday on Twitter that he "couldn't be happier" that Simmons had been elected to join him in the hall, calling him "the definition of a catcher, tough and durable."

The definition of a catcher, tough and durable. He stood above others with clutch hitting for power & average. I couldn’t be happier! Proud to have him join us in Cooperstown. Welcome to the @baseballhall Ted Simmons! — Johnny Bench (@JohnnyBench_5) December 9, 2019

Simmons and Miller will be inducted into the hall in Cooperstown, New York, on July 26 in a class led by the former New York Yankees shortstop Derek Jeter.