Jason Guthrie is the son of J.T. Guthrie, the man who had hidden Stan Mizer's water powered car.
When he encountered Langly and Bond, he seemed overly unfriendly towards strangers and eventually pulled a rifle on them. Only the arrival of Shelly Mizer defused the situation.
His farm was struggling and he would betray those who had sought the water-powered car to Henry Farst in exchange for a large check. The car he directed Farst to was a decoy though.
He refused to deposit the check and sided with the Lone Gunmen in the end.