moeyo, ken!In Volume 6 of Gintama, Sorachi begins revealing early sketches for a few of the main characters in the manga, many of which humorously look like existing characters, not unlike this one here. You might be thinking, "Hey, isn't that the main character Gintoki!?" Actually it is. To quote Sorachi exactly, "It's Gin-san who's got his hair parted and has a certain fire to his eyes. Personality-wise, also a flakey one. Not as lazy as the current Gin-san."
The story goes that Sorachi's original plan was to ride on the coat tails of Harry Potter's popularity and create a manga related to wizardry, but his editor suggested to create a manga based on the Shinsengumi (who were just then receiving a TV drama depicting their tales). He turned his focus on this, with Hijikata Toshirou as the lead character. This was greatly inspired by a movie he watched entitled Moeyo Ken (Burn, my sword!), based off a book of the same name, which dramatizes the life of Hijikata Toshizo, the historical figure Gintama's Hijikata is based off of. Sorachi grew attached to the character design and decided that if he couldn't be the main character, he didn't want him at all, so he created him as a new main character (Gintoki) and cast the Shinsengumi to play the role of "Zenigata in Lupin". (Zenigata and the ICPO play a second role to Lupin, similar to the way that Hijikata and the Shinsengumi often play against Gintoki and the Yorozuya.) Therefore, Hijikata's original design took the form of Gintoki, and from what we can gather, Hijikata became what he is today.