"He was always supportive of artists. He always gave you a fair shake," said Chicago native John Cusack, who appeared with his sister and fellow actor, Joan Cusack.
Ebert worked at the Chicago Sun-Times for more than 40 years. The day before his April 4 death, he wrote in a post on his blog that he was taking a break from his schedule of almost-daily movie reviewing because the cancer had recurred.
"He was simply one of the finest men I ever met," Chaz Ebert said of her late husband during Thursday night's memorial.
Roger Ebert won national fame when he teamed with fellow film critic Gene Siskel of the Chicago Tribune in 1975 for a television show that had them each give a thumbs-up or thumbs-down rating to the latest releases.
John Cusack said he and his sister enjoyed watching Ebert and Siskel growing up. "Chicago's lost a great icon but he'll always be with us," he said of Ebert.
Joan Cusack read a letter from President Barack Obama and first lady Michelle Obama. The Obamas remembered Ebert as a "cultural leader."
Earlier, Todd McCarthy, a film critic who has written for publications such as Variety, said a key to Ebert's success was that he was "a populist without prejudice."
"He was neither high-brow nor low-brow," McCarthy said. "In the world of film criticism for 46 years there was Roger Ebert and then there was the rest of us."
Ebert continued the movie review TV show with Sun-Times colleague Richard Roeper after Siskel's death in 1999.
"I felt that as long as Roger was alive a little bit of Gene was, too," said Siskel's widow, Marlene Iglitzen Siskel, at the memorial. She said Ebert had an "unsurpassed body of work."
A choir opened the gathering by singing, "Roger Ebert, we will always love you."
The historic theater was a fitting place for the event. Ebert screened movies there for many years. And in 2005, the city unveiled a sidewalk medallion under the ornate marquee of the theater as a tribute to Ebert.
Next week, Ebert will be honored at Ebertfest, his annual film festival in Champaign.
He earned respect for championing small independent movies that he scouted out at film festivals while at the same time taking Hollywood's biggest names to task when they missed the mark.
Ebert was the first journalist to win the Pulitzer Prize for movie criticism and was the first critic to have a star on the Hollywood Walk of Fame.