At first he did not wish to teach Aang firebending.  He said he has to first lea to master water and earth before even attempting to lea fire.  Aang confronted him and he told him a whole tale about destiny, something about a fish and the ocean.  But, after a brief blast from the spirit world, namely Avatar Roku, Jeong Jeong decided to help the young airbender out after all.

He then proceeded to teach Aang.  He has such teaching techniques as leaving you alone for hours in a squatting position just breathing, trying to keep a small blaze, not even a blaze, a mini-blaze, from reaching the ends of a single leaf and some other interesting things.

Aang does not see the point to Jeong Jeong’s methods of madness.  But eventually he came around after “the incident.”

Jeong Jeong told Aang and the others to leave immediately once Zhao and his fire nation troops had arrived.  Did I mention Zhao was Jeong Jeong’s student back in the day?  No?  Uh, whoops.  Oh well, now you know. (if you didn’t already)

Before breaking ties with the fire lord, Jeong Jeong was either an Admiral or a General in the fire nation military, somewhere very high up there anyway.  But he determined savagery and was not how he wanted to live his life.

Jeong Jeong is a master firebender.  He knows all there is to know about fire, but, unlike many other firebenders, Jeong Jeong recognizes what fire can do to a man, how it can corrupt him and “embrace savagery.”  He recognizes that the burden placed on a firebender is far greater than any other element, because fire is alive and burns even without a bender.  There is an extra responsibility there that Jeong Jeong sees and, for some reason, no one else does.

On the outside he might appear to be a harsh old man, but in reality Jeong Jeong is one of the greatest firebenders on the planet, and one of the smartest in the world.

Jeong Jeong's wanted poster, located throughout the world; this is what he looked like years ago while he was still with the Fire Lord