JK is a guy who likes to play games and make you feel at home. According to him, there's very few things as exciting in the world as having a fun gaming afternoon with your friends and that's exactly the feeling he's trying to accomplish. This means that he'll do anything, as long as it's fun: gaming, programming, singing, playing instruments (ocarina and saxophone), drawing or just plain chatting. This variety of content led him to call himself a "Jack of all trades", which was also the inspiration to calling his viewers "Jackies". He's no expert in any area, far from it, but as long as both the viewer and JK are having fun, he'll do anything.
JK is a normal human. However, when asked about lore, JK will usually just send you this link: https://i.postimg.cc/w60c4ND2/Haha-auto-portrait.jpg?dl=1