His mother was Italian and named him after Leonardo da Vinci, favoring the original spelling of the name. He was an ensign on the Enterprise during the Borg encounter in the year 2373, in which many of the crew were assimilated, including his friend Joel Azaria, whom he was forced to kill.
In 2380, now holding the rank of lieutenant, he was promoted to chief of security on the Enterprise. He was briefly romantically involved with his predecessor, Lieutenant Sara Nave. He was assimilated by the Borg during a mission. He was killed by a fall while grappling with Nave aboard a Borg cube. (TNG novel: Resistance)
On the TrekBBS forums (thread no longer available) author J.M. Dillard stated he pictured actor Tom Welling when writing for this character.