Eliot Seide, the powerful leader of one of the state’s most important unions and a kingmaker in DFL politics for a generation, will retire at the end of October, he said Wednesday.

Seide has been executive director of the Minnesota chapter of American Federation of State County and Municipal Employees, or AFSCME, since 2002. Its 43,000 members have long been a crucial base of support for the DFL.

“He’s a tireless advocate for his members, and he has that New York edge to his style but believes fiercely in doing what’s right for his members,” Gov. Mark Dayton said. The DFL governor said securing the AFSCME endorsement in the fall of 2009 changed the trajectory of his campaign for governor, which many at the time saw as a long shot.

Republican critics of government unions like AFSCME say members’ dues are poured into the campaigns of friendly DFL politicians, who in turn give the unions generous contracts. New taxes and spending lead to more government union workers, which leads to more campaign contributions, and on and on, goes the Republican argument.

Rep. Pat Garofalo, R-Farmington, was on the opposite side of Seide in numerous fights at the State Capitol, including a brutal battle over unionizing child care workers and a series of spending and budget disputes. But he tipped his cap to the labor leader: “While we disagree on many issues, you always know where Seide stands. He has been a passionate advocate for what he believes is right,” Garofalo said.

Once the tributes die down, Seide’s retirement will leave a hole in a labor movement that faces an existential crisis in the next election. If Republicans hold the state House and win the governor’s race, it would give them full control of state government for the first time in decades — likely ushering in an era like Wisconsin under Gov. Scott Walker, where public unions lost collective bargaining rights and saw massive declines in membership, money and political influence.

It is just this outcome that Seide fears and has tried to position AFSCME to prevent, he told the Star Tribune.

“The corporations and the right wing are sophisticated, well-funded and they are ruthless about their desire to wipe unions out of the public sector and out of the scene in America,” he said.

Seide has worked for AFSCME for 39 years, a champion of public workers and the taxes required to pay them during a time of growing anti-labor sentiment by Republicans in both Minnesota and around the country.

“I believe workers should have a voice in the workplace,” Seide said. “If they play by the rules and are working they ought to have a decent life and have health care and should be able to take care of their families. And if they work their whole lives they ought to be able to retire in dignity, not in poverty.”

As some children seem destined by nature and nurture to be musicians or athletes, so Seide was cut from labor cloth, including the garment workers union to which his grandmothers belonged. His Jewish grandparents arrived as immigrants from Eastern Europe, in steerage.

“It was table talk growing up,” he said.

“My father cleaned up a mess,” Seide said of his father’s local printers’ union. “And he taught me you need to have the trust of the workers, and that means protecting the integrity of the union.”

In other words, the corruption that beset some unions had to be cleaned up.

Seide was the first in his family to go to college. He graduated Phi Beta Kappa from New York University.

He arrived in Minnesota in 1980 and was a strike field coordinator just a year later. He became AFSCME’s legislative director, building influence that would make him a feared presence at the Capitol. When Seide showed up at the Capitol looking to make a point, he usually had thousands of green-shirted workers in tow.

After a stint in New York, he returned to Minnesota at a critical time. In 2002, Republican Tim Pawlenty was elected governor as the DFL reeled from the death of Sen. Paul Wellstone.

Seide, who earned $124,000 last year, oversaw the merger of several AFSCME locals into its current iteration, AFSCME Council 5.

He has used the dues to AFSCME to send six-figure checks to the DFL House and Senate caucus campaigns, earning a loyalty that he could count on when the chips were down at the legislative session.

While other unions hunkered down going into the Great Recession, AFSCME spent on technology and the 2010 and 2012 elections, and the results are clear, Seide said: “I’m proud to say we are larger now than when we merged. We are more powerful internally, with better communication with our workers. We are more powerful at the Capitol.”

The union’s board is expected to select a new executive director this month.