Charlie/Marcus Andrews and his Superior Officer

The U.S. Border Patrol appeared in the Season 15 episode "The Last of the Meheecans".

Background
The border patrol officers Charlie(Trey Parker) and Marcus(Matt Stone) sit in their guard tower trying to keep immigrants from Mexico from illegally entering the United States. When Butters, in character as Mantiquilla, inadvertently creates a Mexican revolution, inspiring the Mexicans to abandon their jobs and return to Mexico. This creates a shortage of laborer's causing the border patrol to hire volunteers to keep the Mexicans in the U.S.

Charlie
Charlie is the skinny one with brown hair. He may be the second in charge of their outpost. He is the first to notice the Mexican citizens returning to Mexico.

Marcus
Marcus is the fat one with sunglasses. He may be the leader of border outpost. Marcus comes up with the idea of hiring extra guards to keep the Mexicans from returning to their home country.