Kai.
Kai, along with Cron, is a member of the Centauri police that went to Earth to capture Blackfire. They are techno-organic humanoid crab aliens with a special weapon that extends a capture tentacle that constricts and neutralizes any special superpower of the person who is captured by it. Their probes mistook Starfire for her sister (since they are almost identical; not to mention the fact that Blackfire was impersonating her sister so she could get away with her robberies; also because Blackfire had given Starfire the gem she had stolen). After Robin pointed out that there was another Tamaranean on Earth, Cron and Kai took Blackfire into custody and cleared Starfire of any wrongdoing. They have not appeared in the series since.