The protocol master attending Minister Campio of Kostolain, who polices every detail of his employer's wedding to Lwaxana Troi aboard the Enterprise-D in 2368.
Erko appears in the fifth-season episode Cost of Living. He travels with Campio to see that the marriage is conducted according to Kostolain custom, and from his first moment on the ship he objects: to forms of address, to who should stand where, and to the bride's habit of doing as she pleases.
Lwaxana, who is seldom spoken to in that way, mocks him and ignores him. She prefers to spend her time in a holodeck colony of free spirits with young Alexander Rozhenko, which does nothing to improve Erko's opinion of her.
When Lwaxana comes to the ceremony unclothed, as a Betazoid bride should, Erko declares the affair an outrage and leads Campio out. He was played by Albie Selznick.