Lore

Lore was a Soong-type android constructed by Dr. Noonien Soong circa 2335. While the most successful of Soong's androids to date, Lore exhibited antisocial tendencies which forced Soong to deactivate and disassemble him. Tragically, Lore was first able to contact a Crystalline Entity, which destroyed all organic life on Omicron Theta.

Lore was rediscovered in 2364 by the crew of USS Enterprise-D. Chief engineer Argyle and Dr. Beverly Crusher reassembled and reactivated the android, who then attempted to steal Data's identity and to summon Crystalline Entity to the Enterprise. He was stopped by Data, who beamed Lore out into space. (TNG episode: "Datalore")

Lore drifted in space for close to two years before he was found by a Pakled ship. (TNG: "Brothers")


 * Also aboard the Pakled ship was a version of Data from the far future of an alternate timeline. He hoped to enlist Lore to change his timeline, but found Lore's positronic matrix had been fused during his time in space, and could not be revived.  Data then assumed Lore's identity in order to affect these changes himself. (TNG short story: "I Am Become Death")

In 2367, Lore answered a homing signal intended to draw Data to Soong's new laboratory on Terlina III. There, Lore posed as Data, took the emotion chip Soong had designed for his brother, and fatally injured the doctor. (TNG episode: "Brothers")

In 2369, Lore encountered a group of Borg disconnected from the Collective as a result of Hugh's sense of individuality. Lore established himself as their leader, and directed them to attack Federation targets. This brought the Enterprise and Data to investigate, and Lore attempted to manipulate his brother by broadcasting emotions from the stolen chip. Data, with the help of Geordi La Forge, was able to overcome this influence, and then to shoot and deactivate Lore. (TNG episodes: "Descent, Parts I and II")