Hiroshi Agasa is an inventor and Shinichi's next-door neighbor. He makes his living with a wide number of patents and inventions, including video games _(of which the Detective Boys are enthusiastic test players)._ While many of his inventions are useless or have even damaged his in-house research laboratory, Agasa has been successful enough to live in a large house and even rebuild it when necessary. He has been a friend of Shinichi and Ran since their childhood years.
After Shinichi was shrunk by the APTX 4869, the first person he met and entrusted himself to was Agasa. After having been convinced that the little boy was Shinichi, Agasa was also the first one to advise Shinichi to exercise caution in his pursuit of the Black Organization. He also helped Shinichi in establishing his new identity as Conan Edogawa, including constructing several gadgets which help Shinichi in carrying on his detective work surreptitiously. In order to perfect Conan's cover, he also enrolled him in Teitan Elementary and thus came to know the children who would form the Detective Boys. When Shiho Miyano fled the clutches of the Black Organization, she fled to Shinichi's house but collapsed from exhaustion near Agasa's doorstep. Agasa subsequently took her in, learned about her true identity and helped her establish her new identity as Ai Haibara. He also entrusted Shinichi's parents with the secret about what has happened to their son.

Ever since these beginnings, Agasa has been an invaluable friend for Shinichi and the Detective Boys as a confidant, paternal friend, and someone to hang out with. He often takes the children on trips, most of which turn into criminal cases instead.

Hiroshi Agasa is a jovial, caring and outgoing person and has many friends in his community, a fact which helped him in his covering up of Conan's and Haibara's true origins _(he simply claims that they are the children of his friends and acquaintances)._ Agasa is highly intelligent, having achieved at least one advanced degree and managing to invent a slew of useful gadgets. He is especially proud of his inventions, and their quality must have been recognized, since they have already been used during official events. While a bachelor, he is very paternal and enjoys the company of the Detective Boys. Agasa has a special love for pasta and tomato juice.

By knowing Shinichi and Shiho's identity, Agasa is aware of the existence of Black Organization as well as their crimes. While not confronting them directly, Agasa has been quite active in helping Shinichi and his allies planning against them. Agasa is entrusted by Shinichi when it comes to such cases.

(Source: Detective Conan World)