Butch was an American who was a member of an anti-government militia group in 1996. This group was based outside of Phoenix, Arizona.
After Chakotay and Torres's shuttle crashed in a failed attempt to capture Henry Starling, Butch and his friend Porter who was also a member of the group captured them. They believed that they were government agent send to spy on the militia.
Chakotay and Torres were rescued by Tuvok and the Doctor. (VOY: "Future's End, Part II")