Former state Sen. Michael Johnston, who spent his time at the statehouse crafting some of Colorado’s most ambitious education reform laws, is planning to announce his candidacy for governor Tuesday.

Johnston, 42, will be one of the first Democrats to officially announce a gubernatorial bid. The 2018 race to replace Gov. John Hickenlooper, who must leave office because of term limits, is expected to be a crowded field attracting high profile names from both major political parties.

Johnston’s announcement comes as little surprise. The Democrat has long been considered a contender for the governor’s mansion. And in December, he openly spoke about running.

The Denver Democrat is considered a rising star in his party. He’s been recognized by Time magazine and The New York Times. And he’s well-known in education circles in Colorado and beyond.

But Johnston’s landmark teacher evaluation law, which linked a teacher’s rating to student academic performance, and other efforts has caused friction with the state’s largest teachers union, a large player in Democratic politics.

Other Democrats thought to be considering a run include former U.S. Sen. and Interior Secretary Ken Salazar, Congressman Ed Perlmutter and former state treasurer Cary Kennedy.

Entrepreneur Noel Ginsburg, CEO of Intertech Plastics, also has declared his candidacy and filed paperwork necessary to start raising money. Ginsburg also heads a nonprofit organization that is set to launch a new youth apprenticeship system in Colorado this fall backed by money from Bloomberg Philanthropies and JPMorgan Chase.

Among the high-profile Republicans mulling a run: District Attorney George Brauchler and state Treasurer Walker Stapleton.

Johnston is a former high school principal who got his start in education by joining Teach For America, an organization that recruits college students to teach for at least two years in school districts that serve the nation’s poorest students.

Johnston’s announcement will be at 9 a.m. at the Holly Street Community Center, according to a media release.