An immortal Douwd who lived as a human on Delta Rana IV and destroyed an entire species in a moment of grief.
Kevin Uxbridge appeared to be an elderly man living with his wife, Rishon, on the devastated colony of Delta Rana IV. In The Survivors, the Enterprise-D found their home to be the only thing left after an attack by the Husnock, and the couple refused to leave.
Picard discovered that Kevin was a Douwd, a powerful being who had chosen to live as a human. Rishon had died in the attack, and in his grief Kevin had destroyed every Husnock in existence. He had created the illusions of Rishon and an attacking ship to drive the Enterprise away. Picard left him on Delta Rana IV.