According to Phil Schneider, a geologist and engineer that had a level 1 government clearance, an alien once worked for the US government.
He was called Valiant Thor and he came from Venus. He had six fingers and an IQ of 1,200 and was over 500 earth years old. He was also fluent in more than 100 languages.
He left earth on March 16, 1960, not before warning us that we needed to change our ways.