Riordan, the 39th mayor of L.A., was elected in 1993 and re-elected in 1997. He served until 2001.
While he was mayor, Riordan helped reshape the city after the 1992 riots ignited by the beating of Rodney King. He also helped expand the Los Angeles Police Department and helped in the recovery from the 1994 Northridge earthquake.
Riordan, a Republican who supported abortion rights, saw a drop in crime and a vibrant economy during his tenure.
Mayor Karen Bass released a statement on Riordan's death, highlighting his work.
"Mayor Richard Riordan loved Los Angeles, and devoted so much of himself to bettering our City. He always had a place in his heart for the children of LA, and worked to improve how the City served our youth and communities as a passionate member of the Los Angeles Board of Recreation and Park Commissioners.
Mayor Riordan's legacy includes our City's iconic Central Library, which he saved and rebuilt, and which today carries his name. He also tapped Eli Broad to help get the Walt Disney Concert Hall built.
In the wake of the Northridge earthquake, Mayor Riordan set the standard for emergency action - he reassured us and delivered a response with an intensity that still pushes us all to be faster and stronger amidst crisis.
Though born in New York, Mayor Riordan will be remembered as an L.A. original.
"I extend my deepest condolences to all who loved and looked up to Mayor Riordan. May he rest in peace."
In 2002, Riordan ran for governor, but lost in the primary election. But the former mayor remained involved in L.A., especially by raising money for schools and children's programs.
ABC7 visited the famed original Pantry Cafe in downtown L.A., a Riordan favorite.
"He was friendly with every customer. Every customer would walk in and he would salute everyone. He was a good person, a good man, a good mayor," said Jose Valdez, the general manager of the pantry.
"He would always have a big smile, welcome to every customer," Valdez continued. "On the weekends, he would sit with different families. People loved that. He's going to be missed a lot."
The former mayor released a book in 2014 titled "The Mayor: How I Turned Around Los Angeles after Riots, an Earthquake and the O.J. Simpson Murder Trial."
Riordan died at his Brentwood home Wednesday night, surrounded by his family.