Xelo was Lwaxana Troi's valet. He tried to teach Deanna how to get rid of her English accent.

Lwaxana was forced to terminate Xelo's employment when his thoughts about her became too erotic. (TNG: "Haven")

He was replaced by Homn.

Appendices

Apocrypha

In The Ceremony of Innocence is Drowned, it was revealed that Xelo was actually fired when Lwaxana Troi discovered he had kept numerous keepsakes of her first daughter Kestra. Apparently, she 'nearly fried his brain' before firing him.