CHICAGO (AP) -- Mayor Richard M. Daley, who wielded more control over Chicago than anyone but his father decades before, said Tuesday he will not seek re-election, a surprising end - at least for now - of a dynasty whose surname became synonymous with the city's legendary political machine.

For more than twenty years, Chicagoans grew accustomed to Daley ruling City Hall with red-faced temper, garbled syntax and iron fist. His decision threatens to leave a significant power vacuum in the nation's third largest city, which he helped transform from a gritty industrial hub into a gleaming modern metropolis.

It also opens the door to months of political jockeying before February's election. Among the few names of potential successors to surface before Tuesday was Rahm Emanuel, the White House chief of staff, who mused earlier this year that he might like the post some day.

Flanked by his smiling wife Maggie, who has been battling cancer for years, and their children, Daley called the announcement "a personal decision, no more, no less," and said he and his family now begin a "new phase of our lives." He said he thought about stepping down for several months and became comfortable with his decision during the last several weeks.

"It just feels right," Daley said at a news conference. "I've always believed that every person, especially public officials, must understand when it's time to move on. For me, that time is now.

The Democrat is credited with saving a foundering public school system, beautifying downtown and tearing down the public housing high rises that helped give Chicago its well deserved reputation as one of the nation's most segregated cities, has faced a growing number of challenges and speculation he might decide to quit.

Daley's wife's health has deteriorated in recent months. And the mayor's tenure has been marked by a recent series of high-profile setbacks, from the city's unsuccessful bid to bring the 2016 Olympic Games to Chicago to the U.S. Supreme Court's overturning of the city's handgun ban.

His administration also has been dogged by whispers of corruption, including the 2006 felony conviction of a top aide in connection with illegal hiring practices at City Hall and a department head's conviction this year for illegally handing out city jobs to political campaign workers.

"I described his (tenure) as kind of schizophrenic," said Don Rose, head of the University of Illinois at Chicago political science department. "He was a strong administrator with some bent for reform, but also the Rich Daley raised in the old school of politics that believed in patronage.

Like other mayors, Daley watched as the national recession left his city swimming in red ink. He scrambled to find funds, leading efforts to privatize such money making operations as the city's parking meters to the nearby Skyway.

But with little money coming in, the city is on a pace to empty them years before expected. Combined with unrelenting national headlines about the city's gang violence, Daley's approval rating recently sunk to 37 percent, according to a Chicago Tribune poll in July.

"Given his wife's health and looking down the road where (he sees) 'All I'm going to do is lay people off and raise people's taxes,'" said Richard Ciccone, a former managing editor of the Chicago Tribune and author of a biography of Daley's father. "Do you want to be mayor for that?

President Barack Obama, also a Chicago resident, said "no mayor in America has loved a city more or served a community with greater passion than Rich Daley.

"He helped build Chicago's image as a world class city, and leaves a legacy of progress that will be appreciated for generations to come," the president said in a statement.

Political analysts agreed Daley may have faced opposition for re-election, but likely would have won. He was first elected mayor in 1989, following in the footsteps of his father, Richard J. Daley, who died of a heart attack in 1976 at age 74 during his 21st year in office.

Cook County Clerk David Orr said Tuesday's announcement means "the whole political landscape changes enormously.

"All of a sudden now many of the political people will be focused on the mayor's seat. February is so close," Orr told WBBM radio in Chicago.

Daley's decision leaves an open door for Emanuel, who said during an April television interview that "it's no secret" he'd like to run for mayor of Chicago someday.

Emanuel, a one-time Daley adviser and a Chicago native who was an Illinois congressman until he resigned to take his current White House post, praised Daley Tuesday but refused to say if he would consider a run in February.

"While Mayor Daley surprised me today with his decision to not run for re-election, I have never been surprised by his leadership, dedication and tireless work on behalf of the city and the people of Chicago," Emanuel said in a statement.

Others whose names have surfaced as possible candidates are Democratic U.S. Representatives Jesse Jackson Jr. and Luis Gutierrez, and Chicago Alderman Bob Fioretti.

The fourth of seven children and the oldest son of Richard J. and Eleanor "Sis" Daley, Richard M. Daley grew up in the 11th Ward near the former Comiskey Park, an area of blue-collar bungalows and two-flats, home to many city patronage jobholders as well as judges, prosecutors and police officers.

Politics was a part of family life. A brother, William Daley, would become U.S. commerce secretary under President Clinton and another, John Daley, is a Cook County commissioner.

Richard M. Daley was elected to the state Senate in 1972 and was elected Cook County state's attorney in 1980.

In 1983, Daley finished third in a mayoral primary marred by racial antagonisms. U.S. Rep. Harold Washington defeated Daley and Mayor Jane M. Byrne and became the city's first black mayor. In 1987, Washington died of a heart attack, and Daley won a 1989 special mayoral election.

He has since presided over some of the most dramatic changes in Chicago history, assuming command of the sinking school system in 1995 and replaced entrenched bureaucrats with tough, results-oriented administrators.

He also was the catalyst for a citywide facelift. West Side slums were cleared, new green space was created, a theater district came to life in the north Loop, and Navy Pier became a colorful playground complete with boat rides and a giant Ferris wheel.

Critics have grumbled that in some ways Daley's Chicago was run much as it had been under his father, who was the boss of Chicago's Democratic machine for two decades. They pointed to City Hall scandals and lucrative contracts for the mayor's friends as well as chronic corruption and police brutality cases.

He nevertheless remained popular, winning elections by overwhelming margins. But to some voters, Tuesday's decision made sense.

"He's old, his wife is in ill health. When you strip it all away, he's a family man," said Mark Sherwood, a 61-year-old attorney who works in the city. "There will be a different approach, maybe for the better, maybe for the worse.

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Associated Press writers Sophia Tareen and Caryn Rousseau contributed to this report.