Earth King Homer (often known simply as Homer Simpson) was a notable Earthbender known for his atomic belches that could destroy an entire village, although thankfully he did not use this power to do stuff like that. Although once a simple middle-class guy, he would ultimately become quite the famous figure in both the Earth Kingdom and earthbending history.
Homer Simpson was born in a small town (at least in comparision to the other towns in the kingdom) known as Springfield. Even so, he dreamed of having a better life...apparently he believed that the grass was always greener....no pun intended.
Homer Simpson was married to Marge Simpson (some random woman she found on the Internet with a far higher IQ) and had three kids, two of which were far more intelligent than he was. For a moment it seemed like he had gotten his wish.
Unfortunately, fate would go in the other direction when the Fire Nation came to burn Springfield to the ground Homer Simpson was captured and enslaved by the evil Fire Lord Montgomery Burns along with his partner Waylon Smithers who forced him to work at a power plant using his earth powers. And worst of all, there were no donuts for him to eat.
Eventually Homer Simpson finally snapped after one of the guards ate a donut right in front of him. Suddenly turning green with rage, Homer Simpson used an earthbending ability people had never seen before and laid waste to much of the Fire Nation. Montgomery Burns was not amused and told Waylon Smithers to fire him...and he did, literally. Homer Simpson burst into flames...
The Earth Kingdom were so happy at what Homer Simpson did though that they decided to make him their King so that he could destroy other kingdoms with his power. Yep, that's pretty much what happened. That's all there is to it.