He is the Dragon Leader's sidekick who betrayed him and a ​spoof of Hong Kong action-movie actor Samo Hung. (Source: Gintama Wikia)

Life isn't easy in feudal Japan... especially since the aliens landed and conquered everything! Oh sure, the new health care is great, but the public ban on the use of swords has left a lot of defeated samurai with a difficult decision to make concerning their future career paths! This is especially true if, as in the case of Gintoki Sakata, they're not particularly inclined towards holding a day job, which is why Gintoki's opted for the freelance route, taking any job that's offered to him as long as the financial remuneration sounds right. Unfortunately, in a brave new world filled with stray bug-eyed monsters, upwardly mobile Yakuza and overly ambitious E.T. entrepreneurs, those jobs usually don't pay as well as they should for the pain, suffering and indignities endured! 
(Source: Sentai Filmworks)

The samurai didn't stand a chance. First, the aliens invaded Japan. Next, they took all the jobs. And then they confiscated everyone's swords. So what does a hotheaded former samurai like Sakata "Gin" Gintoki do to make ends meet? Take any odd job that comes his way, even if it means losing his dignity.
 
(Source: Viz Media)
 
Included Bonus Chapters: 
Volume 1: Dandelion (One-shot). 
Volume 2: Shirokuro (One-shot). 
Volume 24: 13 (One-shot). 
Volume 38: Bankara-san Ga Tooru (One-shot). 
Volume 41: Special Lesson.

Debugon