The following contains spoilers for One-Punch Man Chapter 171, "Secret Info," by One, Yusuke Murata, John Werry and James Gaubatz, available in English via Viz Media.
One-Punch Man being a gag manga gives rise to a lot of unique characters, both in terms of appearance and personality. The series has so many idiotic superpowers and villain origin stories that it's difficult to predict what to expect from yet-to-be-introduced characters. One of these mysterious characters finally steps forward in Chapter 171 of the manga.
The fight between the Monster Association and the Hero Association has officially concluded with the abolishment of Garo's divine powers. The Class S hero Metal Knight also takes it upon himself to resolve the battle's aftereffects. He rids the battlefield of any residual radiation and takes care of those injured during the war. It also turns out that he is the one behind the Hero Association's new headquarters, as well as the security system protecting it.
Dr. Bofoi, The Man Behind the Army of Robots
After Saitama lost his place during the Monster Association's attack, he returned to the ruins to scavenge for his lost belongings. It was recently revealed that he was taking residence at the Hero Association's new headquarters. The bald hero was already promoted to Class A, granting him special living privileges. But during one of his excursions, he picked up Overgrown Rover and Black Spermatozoon. The moment they returned to the base, its defense mechanism activated and robot defenders started attacking the monsters. However, Saitama defended his new companions, resulting in multiple destroyed robots.
After the event, a certain individual watched the records of the fight. He discovered that even his level 10 robots, which were supposedly able to defeat two Demon-level monsters, were crushed. That person was none other than Dr. Bofoi, the man donning the hero name Metal Knight. Surprisingly, the scientist looked like a typical, unassuming old man, though his upper teeth were protruded.
Saitama Piques Dr. Bofoi's Interest in Chapter 171
Seeing his proud creation get destroyed logically made the scientist interested in the culprit behind it. Unlike the others who bought the shoddy robots narrative, Dr. Bofoi/Metal Knight only believed in cold facts. He dug into Saitama's information and discovered the Bald Cape's outstanding hero performance. He started as a Class C hero just three months from the present timeline and was immediately promoted just a month and a half later. Even Dr. Bofoi was surprised at how fast this novice hero was promoted, so he made further investigations regarding Saitama's feats.
That's when the doctor discovered something weird. Saitama was present during the world's most threatening events: the destruction of the giant meteor, helping to defeat the Deep Sea King, and the clash with the human monster Garo. And yet, none of his records suggest power beyond normal. Even Saitama's test results during his initial hero assessments merely had a note stating he'd broken previous physical records.
The discrepancy between the footage and the records piqued Dr. Bofoi's interest. Although there wasn't any incriminating evidence just yet, he's decided to keep an eye on the Bald Cape should the novice hero pose a threat to him. As to why a competent hero might be a threat to him, only future developments of One-Punch Man can tell.