The Crystalline Entity was a Brancher, a type of dangerous cosmozoan life-form. Like others of its species it fed on organic matter, converting it into energy, leaving entire planets devoid of life. It was responsible for thousands of deaths over the years. (TTN novel: Orion's Hounds)

In 2336, the Entity was lured to Omicron Theta by Lore, where it fed on the planet, destroying the colony and killing almost all of its inhabitants.

In 2364, after Lore was reactivated by the crew of the USS Enterprise-D, he again summoned the Entity so that it could feed on the ship's crew. The Entity departed after Lore was beamed out into space. (TNG episode: "Datalore")

In 2368, the Enterprise again encountered the Entity, and attempted to discover a means of communicating with it, but the creature was destroyed instead. (TNG episode: "Silicon Avatar")

In 2380, the USS Titan encountered several other Branchers, and repeated attempts at communication using the technique first tried with the Crystalline Entity. The crew had significantly more success and learned to train the Branchers, enabling the formation of a symbiotic relationship between the Branchers, Star-jellies, and Pa'haquel. (TTN novel: Orion's Hounds)