(covers information from several alternate timelines)
Alnschloss K'Bentayr was portrayed by actress Katarzyna Kowalczyk.
Alnschloss' appearance was based on a design by Neville Page. Though the look of the character was similar to Arex from Star Trek: The Animated Series, that was unintentional. "The character of Alnschloss was not inspired nor based on Arex [....] It was based on an original design by [...] Neville Page. JJ liked the design Neville had and asked if I could realize it as a character. It was the first alien to work on first day of shooting and it wowed everybody. It was further brought to life by Kasia Kowalczyk." 
Alnschloss' name comes from production sources and was never mentioned on-screen – and neither was its gender. According to the viral site Starfleet Shipyard, Alnschloss was born on the planet Monchezke in the Beta Quadrant, its service number was SA-890-0404-DB, and it was the security officer. The virtual collectible card battle game Star Trek: Rivals has a card, #5, named "Security Officer A. K'Bentayr".
A cadet named Vel K'Bentayr (β) (possibly a relative) is featured in the 2015 Starfleet Academy comics by IDW. The comic reveals that Monchezkin (β)s came from the Beta Quadrant, and were a hive mind species that rarely communicated vocally, causing them to narrate their actions and feelings aloud when they did so.