He was first encountered by Balk and Ligeti following one of their routine acts of terror upon a hapless Vintaak and Lieutenant Erixon. He was said to have "appeared with startling suddenness right in front of them". This was partially due to Croi's mysterious telepathic ability to stimulate the minds of his "victims", with the end result being a sort of optical illusion. This, as well as his appearance, gained him a reputation as a "ghost".
Croi participated in numerous events aboard the ISS Arcadia from the assault on Bartok to the assault on Khitomer, and ultimately the Battle of Qo'nos. During the infiltration of Ty'gokor by crew-members from the Arcadia, amidst a failed takeover of the ship by Marx and Richtor, Croi was downed and later disappeared from the ship's sickbay. Marx Richtor replaced him as XO.
Mere hours before the destruction of the Arcadia, Croi reappeared to April (at the time transposed into the body of his daughter, Neria) following April's rape at the hands of his daughter (who at the time occupied April's body). Croi claimed to be one of the Overlords who controlled the Empire. (Star Trek: New Empire)
- He was correctly referred to as Commander Croi.
- In Star Trek: New Empire, images of real-life actors were used to represent characters. In this sense Croi Tae'rshan was portrayed by actor Jeremy Irons, as he appeared in the 2002 remake of The Time Machine, which served as inspiration for the character.