Hasegawa used to be an official working for the Bakufu, but after an unfortunate incident with Amanto dignitary Prince Hata, whom he was assigned to serve and protect, his superior asked him to succumb to his shame and commit seppuku, hearing that he ran away from his quarters.
He initially believed that humans should focus on appeasing the Amanto, but after his encounter with Gintoki, his mindset changed, which led to him punching Hata out, thus getting fired. Since then, he has been living a life of somewhat like a loser, getting fired almost every time he gets a new job, mostly due to the unfavourable look his sunglasses and goatee give him.
No matter what, he refuses to remove his sunglasses because it's the only thing he had left to remind him of his successful past. Although he does exchange the sunglasses for a decent pair of half-moon spectacles at one point, he goes back to wearing them after he decides that he is going to live out his life in the best way he can. He is constantly seen working various part-time jobs. He is often referred to as "Madao," short for "marude damena ossan," which roughly translates into "totally useless middle-aged man."
He and Gintoki are on good terms with one another and seem to spend most of their free time gambling. He often plays pachinko, but rarely ever wins. After losing his job for the Bakufu, he is seen doing odd jobs from time to time, like running a supermarket for a friend or driving a taxi at one time.
He's currently estranged from his wife Hatsu, because of his jobless lifestyle, however they still keep in touch.
It is revealed in episode 52 that he is 38 years old after he pees his pants.
