The gorilla king is a boss that can be found near the mini-isle attached to the main Jungle Island. It resembles a large gorilla, though there are noticeable differences, that being the crown it has on its head and the enhancement that covers its fists. It is very Powerful if you are below level 40 grind Gorillas instead if you are below level 40 (this was for my case btw and it worked :))
If one is doing the gorilla king quest, killing it will grant 2k Beli 7k exp and 625 Bounty/Honor.
For newer players, it's going to be a bit hard to defeat the boss without a devil fruit. One way to defeat the gorilla king is to get him stuck on the grass-wedge to the right of where he spawns. Then, just attack him until he's dead, but otherwise, avoid his attacks since they can do 27.7 hp with just a punch.
Be especially cautious of the AoE ground smash attack, as players with low hp can get killed by it in an instant. His ground smash stuns and deals 12.3 damage per hit.
It takes 3 minutes to spawn.