(covers information from several alternate timelines)
The Menk were one of two native Humanoid species on the planet Valakis. They shared the planet with the more advanced Valakians. The Menk were far less evolved than the Valakians, who treated them as lower individuals. However, the Valakians provided the Menk with food, clothing, and other needs.
Humanity made first contact with the Menk in 2151, when the NX-class Enterprise picked up a Valakian shuttle and returned them to their homeworld, where it was discovered that a genetic disorder was slowly wiping the Valakians out. When Dr. Phlox was asked to help, he had a hunch the answer might be in the Menk's immunity to it. His thoughts were correct, but they also found that the Menk were on the verge of an evolutionary breakthrough, showing signs of increased intelligence, which might lead to them becoming the dominant species on the planet.
While several Ferengi later raided Enterprise, one named Muk found a device in the starship's sickbay and, when told to add it to the Ferengi group's collection of stolen goods, he exclaimed "Do I look like a Menk to you?", before insisting that he keep the device for himself. (ENT: "Acquisition")
The Menk had a presence on Earth in an alternate 2259. According to a map seen on a powerwall in the office of Admiral Alexander Marcus, the Menk were located in south San Francisco. (Star Trek Into Darkness, display graphic)
List of Menk