The android serving aboard the USS Enterprise-D is Data.
Data is a Soong-type android created by the cyberneticist Dr. Noonien Soong. He serves as the Enterprise-D's operations officer and later becomes its second officer, holding the rank of lieutenant commander. His positronic brain gives him extraordinary computational ability, physical strength, and resistance to many dangers that affect biological beings.
A central story in Star Trek: The Next Generation follows Data's desire to understand humanity. Although he initially lacks ordinary human emotions, he studies humor, art, friendship, morality, and social behavior. In the film Star Trek: Generations, he receives an emotion chip, allowing him to experience emotions more directly.
Data is often confused with Lore, his unstable and antagonistic brother, or B-4, an earlier Soong android. Lal is another android Data builds, but she is his daughter rather than the Enterprise-D's regular android officer. Brent Spiner portrayed Data, Lore, and B-4.