Data ( Brent Spiner ) is a humanoid android who is considered as a new sentient life form with all of the rights that go with that designation.  Data was created by Dr. Noonien Soong and his wife Juliana Soong at the Omicron Theta colony.  Data was actually the fifth positronic android constructed by Soong.  The first three were unsuccessful, the fourth (Lore) was successful but Soong gave him emotions which were soon discovered to be faulty.  The other colonists were frightened of him so he was deactivated.  

Data had difficulty learning social skills so Dr. Soong built a sub-routine to help out in this area, this is the "Modesty Subroutine".  In addition a creative capacity was also programmed into Data by Mrs. Soong who felt that this would make up for the lack of emotions. After this initial period Data was thought to be unsuccessful and was deactivated.  Then he was programmed with the logs and records of the colony in the hopes it would help him function better in human society.   Before he could be reactivated a Crystalline Entity attacked the colony and Soong and his wife were forced to abandon their work.

Data was discovered in this dormant state by the crew of the USS Tripoli. Data joined Starfleet and first served aboard the USS Trieste.    During this tour of duty the Trieste fell through a wormhole.    Data then transferred to the USS Enterprise.  Data first served in a command post during the Klingon Civil War where his actions led to the uncovering of the Romulan aid to the Duras family and the subsequent end to hostilities. 

Data has shown himself to be resourceful, intelligent, and indispensable to the Enterprise.

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Episodes 13 "Datalore"