The Xarlaxians are a race of unicellular vertebrally challenged trinocular alien creatures.
The less politically correct term for them is "three-eyed gelatinous slime-monsters", but it's considered offensive and only used by species who think they're better just because they have a complex digestive system.
The Xarlaxians reproduce asexually, but still refer to their identical clones as 'family' and claim to miss them when separated over long periods of time. However, the existence of a Xarlaxian King could indicate that this particular specimen is a male and therefore they also have other genders. Unless their definition of 'king' differs from that on Earth, which is also likely and henceforth it might not even mean that the Xarlaxian form of government is a monarchy.
They are relatively fragile and it's possible to deform a specimen into a puddle of cytoplasm simply by penetrating their protective membrane at a high speed, which often causes a SPLODGE sound to occur. They also need to osmose regularly.
Despite having three eyes, their eyesight is fairly inadequate, at least by Earth standards. For example, a Xarlaxian called Grublarr had difficulty in telling Beaver and Steve apart from other left socks, and his colleague needed to check the Socks User Manual to verify his suspicion.
They are technologically very advanced and have displayed the ability to disguise a large battle cruiser as a much smaller washing machine. Such a feat was documented in the 'sock it to me' story arc that ran from Comic 149 to Comic 157.
In the story it was revealed that recently, a new washing machine had been delivered to Beaver and Steve by none other than the Xarlaxian King, who had cunningly disguised himself as the delivery guy. The "washing machine" then proceeded to detect left socks placed within and transport them to Left Sock Storage Depot 04, where allegedly they were used to extract the rare element chizanunium, which fuels their ships and is most commonly found in the left socks of Earth.
This theory is, however, undermined by anecdotal evidence of the Xarlaxians actually having left feet, despite their lack of vertebrae, and enjoying the wearing of 'good left socks' made by the Earthlings. Furthermore, the fact that they chose to steal the socks instead of asking politely arouses additional suspicion.
The Xarlaxians seem to have card games similar to those on Earth, as evidenced by the fact that they were playing a game involving the utterance of the phrase "Go Fish", and a suit called "a set of muscular chambers and valves for pumping oxygen-rich fluid around multi-celluar organisms", which is one way to describe a heart.