One punch man webcomic is a webcomic created by ONE about the the adventures of the hero saitman. This is the original series of the manga One punch man, and thus, is where it gets most of its source at.
The Manga adaptation of OnePunch-Man is illustrated by Yusuke Murata and follows the adventures of Saitama. While being almost exactly the same series in terms of content there are slight variations and the artwork is a much higher quality. The Manga is published by Sheuisha's Young Jump Next and has several volumes to it's name.