Tessic's species was a humanoid race from the Alpha or Beta Quadrant. Members of that race had three protruded cranial ridges on the forehead, from which some strands of hair was grown. These strands seem to be shorter or weaker on older males with balding hairline.
In 2152, they operated a ramshackle deuterium mining colony on an isolated planet under the administration of Tessic. When NX-class starship Enterprise visited the colony to trade for deuterium in that year, the colonists were under duress from Klingon marauders, which the colonists reluctantly demonstrated to the Enterprise officers. They were poorly trained or equipped to defend their quarry, so the Klingon Korok had been extorting their resources for some five seasons with threats of violence.
Enterprise Captain Jonathan Archer offered Tessic aid to teach the colonists to defend themselves so that they could win their freedom from the bullying Klingons. With assistance from the Enterprise crewmembers, the colonists moved mobile structures to expose the volatile plasma extraction pumps – with a view to trapping the Klingons there – and learned how to use firearms as well as how to combat the Klingon bat'leth. When the Klingons returned, they were drawn into the trap and finally forced to abandon their quarry. (ENT: "Marauders")