A Green Giant is gone. Mike Butler, who would dye the Chicago River green each St. Patrick’s Day, has died.

Mr. Butler, stricken with dementia, died Tuesday of pneumonia, his family said. He was 81.

For three generations and more than half a century, every St. Patrick’s Day has seen the Chicago River turned green for the day by Mr. Butler’s family and another clan of volunteers, the Rowans.

Mr. Butler took his role very seriously.

“We never let anybody else know exactly what we do beforehand and during the process to get a completely green, Irish river,” he once said.

“He was very, very secretive about the dye,” said his daughter, Kathleen Unes.

After he’d pick up the powder each year, “It was hidden in the garage,” she said.

“He’d say, ‘I’ll take it to my grave,’ ” Unes said of her father’s secret process.

But Chicagoans won’t have to worry about the river dye-ing dying. The Rowans know the source of the nontoxic powder, according to Tom Rowan.

“We always refer to it as ‘leprechaun dust,’ ” Rowan said. “We have never told anybody what it is.”

He described Mr. Butler like this: “Mike was the type of guy, you could call him at 2 o’clock in the morning and say you were broken down in Milwaukee, and at 2:15 he’d be heading up to Milwaukee to help you.”

Though Mr. Butler loved being a river dye-er, uneasy lies the head that wears this green crown. The project is a consuming one. Arrangements must be made for boats, and for cranes to lower them into water.

And each year the St. Patrick’s Day crowds grow. Mr. Butler didn’t want to disappoint them.

After turning the river green, he’d sometimes ask a priest for dispensation to break his Lenten fast, during which he would abstain from drinking. Permission given, he’d treat himself to a Jameson’s Irish whiskey to congratulate himself on a dye job well done, his family said.

Mr. Butler grew up near 87th and Ashland in St. Kilian’s parish, said another daughter, Michelle Butler-Mingey. His mother was from Roscrea, County Tipperary, and his father from County Kerry. He went to Leo High School and Loyola University, where he earned a master’s degree in political science.

The Butlers were friends of the Daley family, and Mr. Butler was an assistant to then-18th Ward Ald. James C. Murray. He worked under seven mayors in a variety of City Hall roles, including assistant port director and with the Department of Streets and Sanitation. In his last job, he was a traffic engineer, according to his wife, Marlene Butler.

For a time, he headed the city’s “Snow Command,” helping develop the winter parking ban on main streets. During bad weather, “He never came home for a month,” said Michelle Butler-Mingey.

Over the protests of his children, who longed for snow days off from school, “He would always, always make sure our street got plowed,” said another daughter, Patricia Hansa.

He met the former Marlene Vyneman, a Quad Cities native, after she arrived in Chicago to work as a nurse.

“He swept me off my feet, his Irish charm,” she said, and they got married nine months later.

Chicago’s river-dyeing tradition began in 1962, though its genesis is a bit murky. Most versions lead back to the sponsor of the St. Patrick’s Day parade — the Chicago Journeymen Plumbers union.

“Daley wanted something spectacular” for the holiday, Marlene Butler said of Mayor Richard J. Daley.

A light-bulb moment happened when somebody spotted a plumber splashed with green stains from a substance used to check for leaks, she said.

The Rowans and Butlers figured out the best way to distribute the dyeing powder — which is orange — was by shaking it through old-fashioned flour-sifters. Then came the next step, a second boat — “the ‘Mixmaster,’ ” according to Marlene Butler. When churned with water, the orange dye turns the water a phosphorescent green.

The orange-to-green metamorphosis led to some nerve-wracking moments when Mr. Butler and his son, Mark Butler, flew to Dublin in 1998 to dye the River Liffey for St. Patrick’s Day. When spectators in Catholic Dublin saw the initial orange dye, they booed, Rowan said.

“They thought it was some kind of Protestant protest against the Good Friday [peace] agreement” between Catholics and Protestants, said Gary Flood, a producer of the Dublin St. Patrick’s Day festival. In Ireland, green is a Catholic color. Orange represents Protestants.

Luckily, some nearby jet-skiers churned the Liffey. “It started to turn green, and they started yelling, ‘Peace,’ ” Michael Butler told the Sun-Times in 2010. The crowds cheered.

Flood calls Mr. Butler “the living definition of the Irish who are hugely proud of their heritage.”

“It’s special,” Mr. Butler once said of the St. Patrick’s Day tradition. “We’re the only city in the United States that does it. Nobody has been able to quite duplicate it. Other cities have tried. Maybe they get a little color in, but they never succeed the way we get the Chicago River.”

Even more than St. Patrick’s Day, though, Mr. Butler loved Christmas.

“Every Thanksgiving, he and I would get up really early,” said another daughter, Jennifer Kearns. “We would watch Macy’s Thanksgiving parade, and I would sit on his lap and look at the Sears Christmas catalog.”

He had a succession of Irish terriers — Clancy, Dingle, Murphy, McGinty and Mickey. Mickey was a comfort as his memory failed. Last Sunday, as he rested at the Birches memory-care facility in Clarendon Hills, his daughters showed him Mickey’s latest trick on a cellphone. “He kept asking to see it,” Jennifer Kearns said.

Perhaps because of his days with Snow Command, “He was obsessed with the weather,” said another daughter, Erin Horath. “Tom Skilling’s phone number was on his phone.” When Butler weddings were looming, “My dad was calling Tom Skilling to check on the weather.”

Mr. Butler’s son Mark died of cancer in 2010. It was a raw blow to his determined and loving father, relatives said.

“He was the type of man who never took no for an answer,” said Patricia Hansa. “He always knew somebody who knew somebody.” But, with Mark’s death, she said, “There was no negotiating or somebody he knew who could fix it.”

Mr. Butler is also survived by 14 grandchildren. His funeral was Saturday at Our Lady of Mount Carmel in Darien.