A United States ambassador, Joseph Faxon never expected to be the representative of the U.S. to an alien species, the Aschen. Young, but experienced, the ambassador successfully led negotiations with the alien species until they were cut short by a crucial discovery.
The Aschen were in possession of technology capable of rendering an entire population sterile in a matter of years. After this was discovered, he and Samantha Carter proceeded to thwart the alliance, and the Aschen's capabilities of conquering Earth.
Faxon sacrificed himself to allow Carter to escape through the Stargate from the planet Volia, cutting off his retreat behind her with the iris, which closed in time to prevent a deadly biogenic weapon from reaching Earth. It is not known whether Faxon is alive or dead.
In an alternate future which was prevented by SG-1, Faxon married Samantha Carter and attempted on several occasions to father a child, each without success. Dr. Janet Fraiser's discovery of Sam's sterility was the key reason that Sam led the mission to alter history, to try and prevent Earth from ever encountering the Aschen.
2010 - In an alternate future, Joe is married to Samantha Carter, and serves Earth as ambassador to the Aschen -- who turn out to be en enemy masquerading as a friend.
2001 - SG-1 encounters the Aschen, and Faxon is sent to conduct preliminary treaty negotiations -- but sacrifices himself so that Sam can escape when the Aschen's true purposes are revealed.