2. Genos

If Saitama wasn't so goddamn awesome, Genos would be the obvious No.1. Genos is a cyborg, and first appeared in S1 E2, and serves as a minor protagonist in the show. In the following episode, Genos becomes Saitama's student after witnessing his endless power and strives to be just like his master.

While Saitama was forced to start from C-Class, Genos was promoted to S-Class Seat 17 immediately, making him one of the strongest heroes in the world from the get-go.

It is often forgotten, but Genos does have his motives other than noble to be a hero. When he was 15, a cyborg attacked his hometown and killed everyone in the area besides Genos. This incident inspired hatred for this cyborg within Genos, and gave him the motivation to get stronger so he can inn-act his revenge.

Genos is consistently receiving upgrades to his body. and has rapidly became one of the strongest heroes in the world, proved by his ranking as the 10th Seat in S-Class (accurate as of S2 E3). Genos' interactions with Saitama and other characters is a source of humor due to his stoicism and general emotionless demeanor.