When Gary T. Johnson took over as Chicago History Museum president in 2005, he considered himself “lucky” to lead one of the city’s best-known cultural institutions.

“I had been the kind of lawyer who took an interest in nonprofits, especially civil rights organizations,” Johnson said. “I had experience in the nonprofit community, a love of history — and especially Chicago history. And so I was lucky enough to be hired from such an unusual background.”

Johnson, who notified the museum Wednesday of his retirement, plans to hand over the reins by January 2021, or whenever his successor is hired — a process that can take up to 10 months, he said.

Under Johnson’s watch, the museum rebranded, changing its name from the Chicago Historical Society to the Chicago History Museum.

“We became the Chicago History Museum because we thought that was a more welcoming name, whereas the Historical Society sounded like it was a private club,” Johnson explained.

The museum, at 1601 N. Clark St. in the Lincoln Park neighborhood, preserves the city’s history through artifacts, documents and images.

Under Johnson’s leadership, the museum greatly expanded its photo collection, and, in 2016, it was honored with the National Medal for Museum and Library Service — the nation’s highest award for museums and libraries.

“Gary tackled reinvention the day he took this position,” Walter Carlson, chairman of the museum’s board of trustees, said in a statement. “The next president will be a person who can build on Gary’s commitment to the community and to the idea that a museum must continually reinvent itself.”

Johnson said what he’ll miss most about being at the helm of the museum is the level of unpredictability his “dream job” brought him over the years, along with speaking to children about the city’s history.

“When you have so many different activities and the subject is Chicago, you never know what you’re going to deal with in a given day,” Johnson said.

The museum’s Board of Trustees has hired the executive search firm of Isaacson Miller to help identify candidates for Johnson’s successor.