When he leaves office next spring, Daley will have served about five months longer than his father.
Between them, the Daleys have been in charge in Chicago for 42 of the past 55 years.
Last week, at the first-ever ceremony to name a building after Richard M. Daley and first lady Maggie Daley, the mayor said time in office should not be the measure of greatness:
"It's not the time you put in, it is the passion you that have given to your years of service," said Mayor Daley.
The now longest-serving mayor insisted the greatest Chicago mayor of all time remains his father, Richard J. Daley, whose controlling and passionate 21-plus years of leadership continued through the turbulent 1950s and 1960s, lasting until 1976.
"Think of his great dedication," said Daley. "He died in office and if it wasn't for that, he'd be the longest serving mayor of our city."
The case for Richard M. Daley as the greatest will be argued. After winning a 1989 special election to finish the term of Harold Washington, who died in office, Daley worked to heal the city's deep racial divisions.
"I'm not interested in running as a white candidate or in serving as mayor for half the people," said Daley at the time of the campaign.
He oversaw a downtown office and residential building boom, had the vision for Navy Pier, Millennium Park and the south lakefront, while tearing down what had become wretched public housing projects built during his father's terms in office.
"I think he took his father's vision and made it his own," said Chicago Library Commissioner Mary Dempsey. "That is, while his father was also a marvelous builder and was responsible for the vitality of this city, he's made this into a world-class city."
Momentum slowed as the great recession took hold in Chicago and the city lost its bid for the 2016 Olympics. To avoid tax increases, the mayor encouraged selling off municipal assets, including backing the flawed deal for the parking meter system.
While Daley built dozens of public school buildings, his critics question the mayor's constant claim that under his leadership, Chicago's public education system has improved.
"How much improvement can there really be when almost half the kids drop out of school and don't graduate?" said Congressman Danny Davis, one of the candidates hoping to replace the Daley.
For all but 12 of the last 55 years, Chicago has been led by a Daley. As for the future, the mayor has not encouraged any of his own offspring to run for elective office.
"They have to make their own decision. My dad never encouraged me," said Daley. "My Dad said you make your own decision if you want to go into it. Never push your kids into something they don't want to do. Too many people do that in life and they regret that later on in life."
If Richard M. Daley serves until the last day of his term, May 16, 2011, he will have been Mayor of Chicago for just over 22 years, a record that is certain to stand for at least a generation.