Saitama obtained his power through a rather unconventional way. He simply trained non-stop, doing mundane exercises like push-ups, sit-ups, and running. This extreme dedication transformed him into the powerful being he is now. It's a simple yet unique origin story.
Deadpool got his powers through a messed-up experiment. His body was subjected to a procedure that gave him superhuman abilities, but also left him scarred and crazy.
The Hulk got his powers through a gamma radiation accident. Bruce Banner was exposed to a huge dose of gamma rays, and that's what transformed him into the Hulk when he gets angry.
Morbius gained his powers through a failed experiment aimed at curing his rare blood disease. The process transformed him into a vampire-like being with enhanced strength and other abilities.
Deadpool got his powers through a rogue experiment. A weapon program tried to give him enhanced abilities, but it went awry, resulting in his unique powers and messed-up appearance.
Kraven got his powers through a combination of genetic enhancements and intense training in the wild. He developed enhanced strength, speed, and senses.