Starting as an enlisted man over twenty-five years before meeting Team Avatar, Fong originally fought against the Fire Nation on the front lines where his "no fear" attitude won him high praises from his superiors. Fong worked his way up the ranks, eventually becoming an officer. He was different from the other officers, having a less formal education, but this set him apart and helped him on his path to becoming a general. Since General Fong started at such a low rank, the men under his command considered him one of their own and they were extremely loyal to him.
In 100 ASC, General Fong was given the responsibility of providing Aang and company an escort to the Earth Kingdom city of Omashu. Bent on stopping the Hundred Year War, during Aang's stay at his fortress, he informed Aang that if he could just trigger the Avatar State, he could defeat the Fire Lord and end the War immediately. After many failed attempts at triggering Aang's Avatar State, he decided that he would have to activate it using force by putting Aang in genuine danger. To this end, he directed his soldiers to attack the Avatar.
The soldiers' attack on Aang did not succeed in triggering the Avatar State, so Fong fooled Aang into believing he had killed Katara by burying her underground. This caused Aang to enter the Avatar State after all, much to his satisfaction but also his fear. Afterwards, General Fong was knocked unconscious by Sokka after he stubbornly thought of more plans to trigger the Avatar State.