[The Colonel]

If whoever was operating the teleport gun was sufficiently trigger happy you could even introduce several factions of humans - the player faction (mixed) and one or more competing factions who are determined to carry on the war - perhaps a German faction determined to finish the battle and eliminate the entire allied presence and an Allied faction lead by someone determined to colonise Mars. Thus as well as the Martians the players can bang heads with other humans - who probably regard them as traitors - and the diplomatic chaos they create with Martians whose first encounters with humans were with dangerous fanatics.