An alien who on Earth takes the form of a pug. Very enthusiastic and full of snappy one-liners, Frank has since joined the prestigious Men in Black Agency.
Frank the Pug was not in the original Men in Black comic--his first appearance was in the 1997 film Men in Black. He has since appeared in most of the subsequent comic books, films, and TV programs related to the Men in Black universe.
The pug Mushu played Frank in the first and second movies (he died before they filmed the third movie. For the second film, he had to have hair dye applied to his whiskers, which had gone gray.
In Men in Black, Frank has only a brief role. Agent K and Agent J go to a kiosk run by an alien to find out where the Arquillian galaxy is. Agent J, who is new to the job, mistakes the elderly, expressionless man running the kiosk to be the alien's disguise and remarks "Not that's the worst disguise ever!" Frank, who is posing in the man's arms pretending to be a pet, swiftly responds "If you don't like it you can kiss my furry butt!" Frank then informs K and J that the galaxy is on Earth and that humans need to understand there is more to the universe than meets the eye.
Frank has a far larger role in Men in Black II. He is now working for the Men in Black. When Agent J admits he has neuralized (mind wiped) another poorly chosen recruit, Zed--the Men in Black chairman--decides to place him with a non-human partner. The partner then turns out to be Frank.
Frank and J investigate a murder at a pizza shop by the alien Serleena, but J--still uncomfortable since Agent K left--is irked by Frank's incessant talking. Frank and J then go to retrieve Agent K from retirement because he has information regarding the location of the Light of Zartha. When Frank and J bring K back to Zed, Zed says J and K are now partners again. He then gives Frank an important job in his office.
When Serleena raids the Men in Black headquarters, Frank manages to hide. He is eventually discovered, but then K and J raid the place looking to rescue the Light of Zartha, which Serleena captured (and will soon be activated and destroy Earth). Frank aids K and J in the battle and manages to help them send the Light off from Earth and destroy Serleena.
In this non-cannon Men in Black TV series, Frank has a similar role to that in the first film. He works at the kiosk finding information for aliens and Men in Black while pretending to be a simple pet to passing by humans. His "owner" is revealed to be a robot. In one episode, Frank's true form is revealed--it turns out to still be rather dog-like, albeit with green skin and insect-like appendages.
Frank is not a real pug, but is in fact a member of the alien race known as Remoolians. His true appearance has not been shown in the films, but was shown in the non-cannon TV show Men in Black: The Series. There he looked like a pug with antennae, extra-eyes and appendages, and green skin.
Frank is famous for his impudent, humorous one-liners as well as being one of the few non-human members of the Men in Black.