When Martok first tried to get officer status (long ago) Kor denied him it because Martok came from a "common" house. With the mark of Kor on his record he couldn't even become a common soldier. He served five years as a civilian laborer on some General's ship until the Romulans attempted to board the ship and he finally got a battle field commission (Source Once More Unto the Breach).
Around 2372, Martok was abducted by the Dominion and replaced with shapeshifter. From The Way Of The Warrior, Part I to In Purgatory`s Shadow we only saw the shapeshifter-Martok.
In By Inferno's Light, Martok escapes and returns to the alpha quadrant with Garak, Worf, and the Bashir, and Martok is made commander of the Klingon forces on Deep Space Nine.
Shortly before the end of the Dominion War (When It Rains...), Gowron came to Deep Space Nine to induct Martok into the Order of Kahless (a great honor), and then announces that he (Gowron) will be taking control of the Klingon forces (formerly controlled by Martok) because it's time for him (Gowron) to "take a more active roll in the war".
However, it becomes clear that Gowron is simply worried about Martok getting too powerful politically, and intends to lower Martok's standings by sending him into battles that he cannot win.
Worf tries to convince Martok to challenge Gowron, but he refuses so Worf kills Gowron himself and, rather than accept the title of Chancellor himself, gives it to Martok. (Tacking Into the Wind)
In 2375, Martok, leading the Klingon fleet, Sisko, leading the Federation fleet, and the Romulans launch a final strike against Cardassia Prime and when the Cardassian fleet joins their side, the Dominion is finally defeated. ((What You Leave Behind)
Played by J. G. Hertzler
This writeup is licensed under the GNU Free Documentation License.