Porter was an American who was a member of an anti-government militia group in 1996 that was based outside of Phoenix, Arizona.
When Chakotay and Torres tried to beam Henry Starling onto their shuttle, which they had disguised so that it would not be picked up on RADAR, the shuttle crashed and Porter and other members of the group captured them. They believed that the Starfleet officers were actually government agents sent to spy on them.
Tuvok and The Doctor rescued them from Porter and his group. (VOY: "Future's End, Part II")
Porter was played by actor Clayton Murray.