Trengur was a shrewd dictator on Oorego IV, but ended up being deposed and placed in an asylum. He was diagnosed as incurably insane.
In 2267, he escaped and fled to Gateway. Once there, he traveled through the Guardian of Forever and posed as a fellow Carthaginian to help Hannibal cross the Alps to invade the Roman Empire. After eliminating Roman troops to their rear, Trengur killed Hannibal and assumed command of the troops, then headed onward to Rome. In the altered timeline, the American Revolution failed in 1776 and the Nazis conquered North America in the 1940s. Trengur subsequently used the Guardian to assume dictatorial control of Earth by the mid 21st century, known to the populace as “The Trengur”.
Using the Guardian, James T. Kirk, Spock and Leonard McCoy went back in time and were able to capture and arrest Trengur before he influenced Hannibal. Afterward, all four returned to the prime universe. The USS Enterprise headed for Oorego IV to return Trengur to the authorities. (TOS comic: "No Time Like the Past")