The android created by Data to be his daughter.
Lal is an android created by Data in The Next Generation, built as his attempt to have a child. She is a self-designed android with a more fluid, adaptable body, and Data guides her through learning how to speak, move and understand social customs.
She quickly picks up skills and begins to develop emotions, a surprising result that Data himself has been unable to attain. When Starfleet attempts to take custody of her for study, Data fights to keep her, believing in her right to live as an individual. Her positronic brain, however, suffers a cascade failure, and she dies despite Data's attempts to save her.
Lal's brief life leaves a lasting mark on Data, who carries her memories, and she stands as an affecting exploration of parenthood, personhood and loss.