DENVER — A former Republican senator is kicking off his gubernatorial bid Tuesday to challenge Democratic Gov. John Hickenlooper next year.

Former Senate Republican Leader Mike Kopp planned to announce his campaign at Red Rocks Amphitheater. The Jefferson County Republican is the fourth Republican running against Hickenlooper, who is seeking re-election.

Kopp served in the state Senate from 2007 to 2011. He resigned his office after his wife died following a long battle with cancer. Kopp now works for Intermountain Rural Electric Association.

Kopp joins Secretary of State Scott Gessler, state Sen. Greg Brophy and former U.S. Rep. Tom Tancredo in the Republican race to take on Hickenlooper.

Kopp also planned announcements Tuesday in Colorado Springs, Fort Collins and Pueblo.

Kopp has a 3 p.m. news conference planned Colorado Springs, at the Mesa Overlook - off Mesa Road overlooking Garden of the Gods.