An exotic and highly intelligent light-green-skinned humanoid from the neutral planet Pandro, whom Starfleet authorized to live aboard the U.S.S. Enterprise for several months as an observer in the hopes of cultivating diplomatic ties with the Pandronians, whose advanced knowledge of medicine could greatly benefit Federation worlds.
Bem, whom Starfleet granted the honorary rank of commander, did precious little observing until the Enterprise crew began surveying the primitive planet Delta Theta III, some six months into Commander Bem's stay aboard the starship. Only after Bem essentially sabotaged a landing party so that he could be captured by the planet's tribal reptilian natives in order to observe them close up did the Pandronian reveal that members of his species are actually "colony creatures," independent lifeforms capable of functioning either separately or as a single entity; this ability enabled him to escape easily from the Delta Thetans whenever he desired.
After being scolded for his actions after the mission by Captain Kirk, Commander Bem considered atoning by permanently splitting up the unity of his body parts, until the disembodied protector of the Delta Thetans convinced him that he would be better off learning from his experiences and moving forward as a unified entity instead.