In 2366 Data built Lal, an advanced android he regarded as his child, who lived for only a short time before suffering a fatal failure.
In 2366 Data used new techniques in positronic programming to build a second android, which he named Lal. Lal chose the appearance of a human woman and began to learn about life aboard the Enterprise-D, soon displaying abilities that went beyond Data's own, including signs of emotion.
Starfleet sent Admiral Haftel, who wanted to move Lal to a research facility. Lal's growing emotions then caused a cascade failure in her neural net. Data and Haftel worked together to save her but could not, and she died after thanking her father. Data transferred her memories into his own neural net.