The Aaziniarzindials - or "Little Green People" as they're known in Federation Standard language (largely because other races constantly stumbled over pronouncing their true name) - are the oldest of the Federation member races. Their interstellar travel technology pre-dates the earliest Human civilizations by several thousand years, and over the millennia their research vessels have visited Earth numerous times to continuously catalogue the evolution of the planet's species.
When it was first discovered that they were the alien species who had been visiting Earth throughout history, there was a great deal of alarm amongst the Human community - with one out-spoken politician even exclaiming during a live membership discussion conference:
"I don't want those green bum-probers anywhere near my nethers!"
The Aaziniarzindial Ambassador was quick to rebut such commentary, publicly assuring everyone in a Federation-wide broadcast that none of the species that they monitored had ever been "kidnapped and rectally violated".
This matter-of-fact statement coupled with their peoples' ever-present geniality, acted as a salve to the majority, helping to smooth the way for the Little Green People to slide almost effortlessly into the Federation, where they have since garnered for themselves a reputation as plucky and fun-loving members of the Metaversal community.