Though Data's strive for humanity and desire for human emotion is a significant plot point (and source for humor) throughout the series, he continually shows a nuanced sense of wisdom, sensitivity, and curiosity.
Data's positronic brain allows him impressive computational capabilities. Data experienced ongoing difficulties during the early years of his life with understanding various aspects of human behavior and was unable to feel emotion or understand certain human idiosyncrasies, inspiring him to strive for his own humanity. Data had a vast array of interests and hobbies - including painting, playing Sherlock Holmes on the holodeck, Shakesphere, music, and games of chance like poker.
In addition to his impressive computational abilities, Data was very strong due to his design. He was easily able to perform physical tasks that even individuals Worf and Riker would be unable to perform.
Data was designed and built by Doctors Noonien and Juliana Soong. He was the fifth android that the pair constructed. The first two prototypes died soon after creation due to unstable positronic matrices. The third android, named B4 was also believed to be a failure and deactivated, this third android eventually disappeared. The fourth android - named Lore - had a stable matrix but a warped, cruel personality. He was deactivated and dismantled, Soong intended to repair him.
The couple then created Data. Data was programmed slightly differently, with a personality that did not include the emotions that had caused Lore to become mentally unstable. At first Juliana and Noonien debated about whether Data should be male or female, Noonien solved that debate by building Data's head in his own image.
Soon Data was activated for the first time. He was very much like an infant at first, struggling with motor control and sensory input. His personality required some adjustment as Data was downright rude. The Soongs were also forced to write a modesty subroutine in order to convince Data to leave his clothes on - Data did not want to wear clothes as he was not affected by the elements, but colonists objected to an anatomically correct android running around naked.
The Soongs then wiped Data's memory and then programmed him with the memories and journals of various colonists.
Soon after Data's creation the Crystalline Entity attacked. Noonien and Juliana fled. At Juliana's insistence Data was left behind as she feared Data would become another Lore. Data was recovered by Starfleet when they responded to the distress call, and reactivated. His life was considered to have begun at that point.
The first few years after activation were difficult for Data as he achieved sentience, the evolution of his positronic brain was hard for him to handle. He briefly considered a form of suicide - shutting down and having his neural net wiped. He later decided to see his difficulties as challenges to be overcame.
Data applied to Starfleet Academy and was accepted in 2341. He graduated in 2345 and was commissioned as an Ensign in Starfleet. Assigned to the USS Trieste, he was promoted to Lieutenant four years later, and to Lieutenant Commander in 2360. Data was recruited for a mission by Captain Jean-Luc Picard, who encouraged him to be more assertive and to go above and beyond in his duties.
Upon the completion of the Enterprise-D in 2364 Data was assigned to the flagship as second officer and operations manager.
In 2371 Data installed an "emotion chip", that his father had created into his positronic net. This allowed him to experience basic emotions for the first time in his life. However an overload caused the chip to fuse in to his brain. Data encountered signifigant difficulties in intergrating his newfound emotions into his program. A couple years later Data developed the ability to deactivate the chip at will if he felt emotions were interfering with his duties, and eventually was able to remove the chip if needed.
Data died in 2379, sacrificing himself to save the crew of the Enterprise-E from Picard's clone Shinzon of Remus. As he had backed up the contents of his matrix into his recently discovered brother B4 before his death, thus Data is "reborn" through his brother.
Data was later resurrected in B-4's body, which allowed the memories and personality to take control of his brother's body. Realizing how important Data was to the Federation B-4 deleted himself so that Data could live again. Working with LaForge and the Daystrom Institute Data had his new body's brain upgraded and re-created the emotion chip.
Afterwards Data returned to active duty within Starfleet, becoming the commanding officer of the Enterprise-E after Picard's retirement from Starfleet.
Following the death of his physical body in 2379 the Daystrom Institute attempted to recover Data's memories from B4's brain. However since his brother's brain was considerably less advanced than his had been, the efforts to retrieve Data largely failed and the Institute felt that much of Data's memories and personality were lost. B-4 was later disassembled and held in storage at the Institute, and was still there in 2399.
However Dr. Bruce Maddox was able to recover a positronic neuron from B-4 that contained Data's memories, and used them to construct a re-creation of Data inside a computer simulation. Data lived within the simulation until 2399, when he was able to talk to Picard one last time and request that his former Captain shut down the simulation, allowing Data to finally die.