Daniel Sutter was an ensign who served as an engineer aboard the USS Enterprise-D in 2368, and father to Clara Sutter. He had been in Starfleet for most of his daughter's life and, since she was two, they had been moved from starship to starship.
He became very concerned when his daughter began playing with an imaginary friend named Isabella, who Clara insisted was real. He brought the child to Deanna Troi for counseling. Troi hypothesized that she was imagining Isabella because she was lonely, she had not stayed on a ship long enough to make any real friends. Both Sutter and Troi were shocked to find out that Isabella was real when she was impersonated by an alien in Human form. (TNG: "Imaginary Friend")