Vorok

Vorok was the commander of a Klingon battle cruiser encountered by in 2151.

He threatened to destroy a cloaked Xyrillian starship when he learned the Xyrillians were using his ship's plasma exhaust to replenish their vessel's teraphasic coils, citing the act as a breach of Klingon security and an act of war.

Jonathan Archer, needing the Xyrillians alive in order to help an impregnated, informed Vorok that the Xyrillians may be willing to share their holographic technology with the Klingons if they were spared. Intrigued, Vorok swore not to destroy the Xyrillians if their technology amused him.

The holographic technology was modified and installed aboard Vorok's battle cruiser, and the Klingon commander kept his word and allowed the Xyrillian ship to return to their homeworld.

Before departing, however, Vorok made it very clear to Archer that if his ship were to encounter the Enterprise again, the Human captain would regret it. 

Vorok Vorok