Jack Bowman is Republican Senator from Montana who is also the Chairman of the Senate Appropriations Committee. He was the Governor of Montana, but he resigned after the Capitol Bombing so his successor could appoint him to the United States Senate. During the events of the series, he continuously opposes Tom Kirkman's ideals.
Before the Capitol Bombing, Jack Bowman was the Republican governor of Montana. He is a staunch conservative who especially has pro-gun views. These views most likely come from being the governor of a conservative, rural state like Montana.
After the Capitol Bombing, he resigned position as governor in order to be appointed as a senator by his successor.