The changeling was able to cause much disruption during its time as Martok. It helped push the Klingon Empire into war against the Cardassian Union in 2372 as well as almost starting a war between the Klingons and the United Federation of Planets.
The other Founders convinced Odo that the changeling was in fact Gowron in the hopes that Starfleet would remove Gowron paving the way for Martok to ascend to chancellor and take full control of the Klingon Empire. However, the changeling was exposed by Odo and was killed in a hail of disruptor fire. The exposure and death of the changeling instead saw a ceasefire agreed between the Klingons and the Federation.