Ian Andrew Troi II was an alien entity who wished to experience human existance. He in the form of a glowing white light entered into Deanna Troi and began his human existance as a fetus. Troi stated a glowing white light impregnated her while she was asleep. Dr. Katherine Pulaski, confirmed the fetus would reach full term within 36 hours. He was born in early 2365 and named after her father, Ian Andrew Troi.
At first Troi did not realize that Ian was an alien. Jean-Luc Picard was first worried that the child could present a danger, but he appeared to be completely harmless. He would grow from an infant to an eight-year-old in one day. At the same time a plasma plague puts everyone on the ship in danger. A contaminated specimen of the hazardous strain has began to grow on the cargo deck due to radiation from an unknown source.
Ian was the source of the radiation. When the young boy realizes this he decides to sacrifice his life to save the crew. As Troi looked on, Ian died but not before he tells her that he was the alien and that he wanted to experience the human life cycle including death. His body reverts to its original state and lift the ship, but not before he had experience humanity, and Troi had experienced the joy and saddeness of parenthood.