Lal was an android, constructed by Data in 2366 with a newly-developed submicron matrix transfer technology. Using his own positronic brain as a template, Data created Lal for two purposes – to attempt to re-create the work of his "father", Noonian Soong; and to experience the act of procreation, and of having a family. Data chose the name for his offspring from the Hindi word meaning "beloved".
Originally genderless and possessing a very basic humanoid appearance, Lal was allowed to choose its own gender and appearance. After narrowing the choices to four – an Andorian female, a Klingon male, and a Human male and female – Lal chose the Human female form. Data wanted her to learn about "being Human", and entered her in the ship's school. Unfortunately, other "children" were afraid of her. As a result, Data decided that allowing Lal to work in Ten Forward would give her more valuable insight into human social interaction. Unexpectedly, Lal began to improve on her father's original specifications, soon becoming able to use verbal contractions and even, eventually, to feel emotions.
However, Starfleet was interested in separating Lal from her father for purposes of study, and when she was only a few weeks old, Admiral Anthony Haftel ordered Data to transfer Lal to the Daystrom Institute annex on Galor IV. According to the Admiral, she was capable of more than 60 trillion calculations per second.
The situation caused Lal distress, and while speaking with Deanna Troi, she began to feel emotional anxiety. Upon running diagnostics, Data identified the problem as a symptom of a cascade failure in her neural net, and, with the assistance of Admiral Haftel, attempted to repair the damage. Despite their best efforts, the effect was irreparable, and Lal's neural net failed, causing her to shut down permanently. As a final act, Data transferred Lal's memories and experiences into his own brain, ensuring a part of her would live on.