Despite being overwhelmingly strong and defeating monsters with just a punch, even he was hopeless against a mosquito.

Despite never getting much recognition as a hero, the fact doesn't change that Saitama's efforts were what led the foundation of Hero Association. 

Saitama's inhuman strength is not really caused by his exercise regime but rather his sheer willpower which made him overcome his limiter completely. 

Saitama's godly power is so insane that just his sneeze alone was able to cause massive destruction on Jupiter. 

Just like Saitama, the creator of One Punch Man also started the series just for fun which has now become one of the best in the industry.

The price that he paid for his strength was not just his hairs but his emotions as well and that is why he seeks thrill to feel human once again.