One of the most unusual living beings in the Federation, Data is a product of the late Dr. Noonian Soong's controversial theories on positronic computing.1 Only four functional positronic brains have ever been known to exist; Data was the first example known to Starfleet, while his 'brother' Lore was the second. After his construction Lore quickly developed an aberrant personality, leading him to bring the Crystalline Entity to the Omicron Theta colony where Soong lived. Soong dismantled lore before the creature arrived; when the colony was destroyed he was forced to flee, leaving Data deactivated on the planet.
Data remained dormant on Omicron Theta until 2338, when the crew of the Starship Tripoli discovered him whist investigating the destruction of the colony. Data initially had few social skills and was regarded as little more than an interesting construct. In time, however, he demonstrated a degree of intelligence and independence which impressed his new masters sufficiently that they allowed him to enrol in Starfleet Academy. Data did not fit in well at Starfleet, but he persevered and eventually graduated1 with honours in exobiology and probability mechanics.2
After graduation Data spent three years as an Ensign followed by "ten or twelve" on varied space duty in the Lieutenant grades.1 However, he continued to struggle for acceptance. It was not until he arrived on the Enterprise-D that he found himself making true friends. This reinforced his own self-image and encouraged him to stop thinking of himself as 'disposable'.3
In 2365 Starfleet Commander Bruce Maddox decided to dismantle Data so he could investigate his function in an attempt to recreate Dr. Soong's work. Data declined the invitation, prompting Maddox to order him to comply. When Data attempted to resign instead, Maddox took the position that Data was the property of Starfleet and so not legally able to resign, a stance disputed by Captain Picard. A landmark legal hearing determined that Data in fact had the right to choose his own destiny. Maddox withdrew the transfer request and Data was allowed to remain on the Enterprise-D.4 After the loss of the Enterprise-D, Data transferred with the rest of his shipmates to the Enterprise-E where he remained Chief of Operations. Here he participated in the ship's efforts to correct the Borg's alteration of Federation history, where he was briefly tempted by the prospect of becoming partly biological through Borg technology. Data ultimately rejected this prospect and was instrumental in defeating the Borg.5
Data continued as operations officer of the Enterprise-E until 2378, when he was to have assumed the First Officer's role after Commander Riker accepted a promotion and transfer. The Enterprise located another Soong android, known as B-4, at this time, a prototype for Data himself which was externally identical to him but considerably more simplistic mentally. Data downloaded his memories into B-4 in the hope that it would help him to develop.
When the Enterprise-E fought the Scimitar to prevent Praetor Shinzon's attack on Earth shortly before Riker's transfer, Data chose to sacrifice himself in order to destroy the Scimitar and prevent it using its Thalaron radiation weapon on the Enterprise-E.
After the battle, Captain Picard found some reason to hope that at least a portion of Data's memories had indeed become active in the mind of B-4. In this sense, at least a little of Data has survived.6
Shortly after his arrival the Enterprise-D also visited Omicron Theta, where a previous Android, Lore, was discovered in a disassembled state. Lore was reassembled, and he and Data regarded one another as brothers. However, Lore quickly began to display psychotic behaviour and attempted to kill the Enterprise crew. Data was forced to beam his brother into space, where he was abandoned.1
In 2366 Data attempted to re-create Soong's work himself and created Lal, a positronic android whom Data regarded as his daughter. Lal initially functioned well, even surpassing her father in many respects. Her positronic brain eventually became capable of experiencing emotion, but this caused a system-wide cascade failure which resulted in complete shutdown. Data incorporated Lal's positronic paths into his own brain in an attempt to preserve something of her personality.7
Data regarded Doctor Soong as his father, and although he believed him to be dead, in 2367 Dr. Soong summoned Data to him with a homing beacon. He offered Data a chip which would allow him to feel genuine Human emotions. However, Lore also followed the homing beacon and arrived, having been rescued from space by a passing ship. Lore stole the emotion chip, which caused him to become even more unstable since it was not designed for him. He killed Soong and escaped.8 Data met Lore once again in 2370, when the android used the emotion chip to override Datas own ethical programming. Data was eventually able to incapacitate and dismantle his brother, effectively killing him. He kept the chip in storage for several years afterwards.9
A few months later Data met Dr. Juliana Tainer, the former wife of Dr. Soong. The two came to regard one another as mother and son, though Data remained suspicious as to her true identity. His suspicions were justified when she was shown to be an android constructed with the same basic technology as Data, though designed to be entirely Human in appearance and behaviour even to the extent of being unaware of her own artificial nature. Data chose to allow her to continue to believe herself Human, and the two parted on good terms.10
Data defined friendship in the following way : "As I experience certain sensory input patterns, my mental pathways become accustomed to them. The inputs eventually are anticipated. And even "missed" when absent."11 He was thus not capable of liking people as such, but did develop a degree of attachment to certain people. His closest friend on the Enterprise-D was Geordi LaForge; the two spent much time together and explored various aspects of Data's mental functioning such as Humour12 and artistic creativity.13
Data was designed to be fully capable of sexual activity and in 2364 Lieutenant Yar seduced him whilst she was suffering from the effects of the Psi-2000 virus. After her recovery Yar dismissed the incident with an embarrassed "it never happened!"14 but Data would long remember the event and regarded Yar as being special to him. For this reason he kept a small holographic portrait of Yar4 after her death on Vagra II.15 In 2367 Data had a brief romantic relationship with Lieutenant Jenna D'Sora. He devoted a considerable share of his internal resources to devising ways to make her happy, even to the extent of deliberately provoking an argument on the grounds that she would feel better once they made up afterwards. In the end, however, she broke up with him when she realized that he could not love her.16 The relationship was brief enough that the two did not engage in sexual activity.17
In 2371 Data installed the emotion chip recovered from Lore. He suffered from considerable difficulties initially18, but was subsequently reasonably successful in integrating emotions into his life. He was also able to learn to shut the emotion chip down when it threatened to overwhelm him.5
In 2373 Data was abducted by the Borg and underwent an attempted seduction by the Borg Queen. She grafted cloned tissue onto his body, enabling him to experience physical sensations in a new way, and offered him a more Human existence in return for his allegiance. Data found the offer so tempting that he considered it for an entire 0.68 seconds, before deciding instead to merely play along before ultimately betraying her.5