Zarthan

The Zarthans are a sapient species from the planet Zartha, which have been in war against the Kylothians for decades at least. In the 1970s a Zarthan delegation including their royal princess Lauranna went to Earth to seek protection for something called the Light of Zartha, which would be of vital importance for the protection of their homeworld against the Kylothians.

Believed by some to be some kind of artifact, it is revealed that the Light of Zartha is actually a person – Laura Vasquez – who is the daughter of Princess Lauranna and destined to become her people's leader. At one point, Agent K implies that Zarthans; or at least the Light of Zartha; may have unconscious influence over the weather ("it rains because you're sad"). This is apparently true as shown at the end of the film where she departs and comes to tears and it start to rain.

Biology
Very little is known of Zarthan physiology, although it is likely that they are externally identical to Humans. It is also possible that they are genetically compatible with Humans.