In 1996, a new Chicago theater named Remy Bumppo Theatre Company made its entrance by declaring it intended to cast the city’s best actors in the most literate works it could find. In that first show, playing the neurotic Ruth, whose subconscious thoughts fuel Tom Stoppard’s “Night and Day,” was Lia Mortensen.

Her presence, and her luminous performance, was a signal that Remy Bumppo had its act together.

Mortensen died Wednesday at Northwestern Hospital from cancer at the age of 57.

She was born on June 15, 1965, and raised in Evanston as the daughter of two prominent academics at Northwestern University. Her late father, Dale T. Mortensen, won a Nobel Prize in economics in 2010. After graduating from Indiana University in 1987, Lia moved back to the Chicago area to act, occasionally on screen but mostly in the Chicago theater. “She got her Equity card at age 24 and never looked back,” said Si Osborne, her former husband.

Mortensen worked constantly in leading roles in the booming 1990s and 2000s world of nonprofit theater in Chicago. At Northlight Theatre in 2002, she played Sally Talley in Lanford Wilson’s “Talley’s Folly,” a character trying to lose enough emotional baggage to fall in love. And in Steve Scott’s 2007 Goodman Theatre production of “Rabbit Hole,” Mortensen gave perhaps the most wrenching performance of her stage career, playing a mother who has lost a young child and must now navigate a new life in unimaginable circumstances.

As was typical with Mortensen when playing characters facing trauma, emotions remained veiled at first, only to spill out with an intensity born at least partly of surprise. Mortensen was a zesty, restless actress, ideally cast as an urbane sophisticate but fully capable of the deepest of dives into a character’s heart. In 2011, she did extraordinary work in a play called “The Big Meal” at Chicago’s former American Theater Company; it was a title that aptly expressed the bounty of one of her performances.

Her favorite role, said her daughter Jesse Osborne, was that of Grace in J.R. Sullivan’s production of Brian Friel’s “Faith Healer,” a huge hit in the 1990s at both the Turnaround Theatre and Steppenwolf Theatre Company.

In 2012, Mortensen returned to the play as the original production was remounted 18 years later. By this time, Lia and Si Osborne, two of the three actors in the cast (along with Brad Armacost), were no longer married. Given the subject matter of the play, mostly about the difficulty of maintaining a personal relationship in the context of an artistic career, both Mortensen and Osborne showed exceptional courage. And it was an aptly intense production.

“When you were on stage with Lia,” Si Osborne said, “you danced like Nureyev, you spoke like James Earl Jones, you thought like Einstein and you moved like the wind. Lia made everyone better than they were.”

“Art really imitated life,” said Jesse Osborne, the couple’s oldest daughter. “I saw ‘Faith Healer’ again and again and I was just stunned that this actress was also my mom. She was just so brilliant.”

In 2016, Mortensen, who had not generally done musicals, left her comfort zone entirely to play Joanne in the Writers Theatre production of Stephen Sondheim’s “Company,” a role for which she seemed too young. But the director, William Brown, set up Mortensen’s character as a go-getter who had yet to learn how the wisdom of age should and can overcome unwise temptation. It was a notably empowered and empowering take on an often-problematic character and a reminder of Mortensen’s comfort with the biggest artistic risks.

“My mama does not want people to be sad,” Jesse Osborne said. “She just wants smiles. What’s the quote my dad likes? Take a good look, for her like will not soon be seen again.”

Survivors include Lia’s mother, Beverly P. Mortensen, her daughters Jesse and Ozzy Osborne and partners Marisol Garcia and Lily Turner. Plans for a memorial service are pending.

Chris Jones is a Tribune critic.

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