Marvin Miller, former executive director of the Major League Baseball Players Association, has passed away at the age of 95. Miller led the charge for free agency, changing baseball forever.

Miller was the executive director of the MLBPA from 1966 to 1982, reports The New York Times. In his time as the union leader, Miller ushered in a new era of baseball, giving players more rights, including free agency.

Born in Brooklyn, N.Y., Miller graduated from New York University and worked as an economist for the United Steelworkers of America, notes Chicago Tribune. During his time as baseball union leader, Miller won better minimum salaries and arbitration to settle contract disputes, which paved the way for free agency.

In the old days, team owners controlled Major League Baseball as well as the players. Contracts gave owners the right to keep a player on the team for his entire career thanks to the reserve clause, which  let a team hold the rights to a player after his contract expired. The only choice for a player was to resign or ask for a trade, which the owner could simply ignore. It was not until Miller was the union leader that the reserve clause was eliminated in 1975 using arbitration to declare Catfish Hunter a free agent.

Free agency has led to the multi-million dollar contracts that players can sign today, notes Chicago Tribune. Free agency changed baseball and all other professional sports in America. Miller in his time as the union leader also improved pension as well as health benefits.

Michael Weiner, current MLBPA executive director, said in a statement, "All players -- past, present and future -- owe a debt of gratitude to Marvin, and his influence transcends baseball. Marvin, without question, is largely responsible for ushering in the modern era of sports, which has resulted in tremendous benefits to players, owners and fans of all sports.”

Players have taken to Twitter to mourn the passing of Miller. Detroit Tigers pitcher Justin Verlander said, “Marvin Miller was an incredible man. We are all grateful for his contributions -- his legacy will live on for generations.” New York Mets pitcher, and 2012 Cy Young winner, R.A. Dickey said “Sad to hear about the passing if Marvin Miller. He will be missed. A true pioneer. Thank you Marvin.”

Red Barber, former broadcaster for the Cincinnati Reds, Brooklyn Dodgers and New York Yankees, famously said, “Marvin Miller, along with Babe Ruth and Jackie Robinson, is one of the two or three most important men in baseball history.”