As a teenager, Komori was bitten by a radioactive spider and was gifted with its powers.
Yu Komori (The japanese name of Spider-Man's alter-ego rather then Peter Parker) used to be a bookworm. He had no athletic ability. Whatever sport he played, he would always manage to screw up. One day after all the other students had gone home, Komori did an extremely dangerous experiment with radioactivity harnessing equipment. By chance, a spider that had been infected by large amounts of radiation given off by the experiment bit him. Countless blood cells in his body were irradiated and the abilities of the spider were passed on to him. With these powers, Komori was granted unbelievable physical strength and jumping ability, his hands allowed him to climb freely up walls, and his feet adhered to things just like a spider.
Komori decided that since he now had the abilities of a spider, he wanted to know more about the limits of his power. So he went to the library every day to conduct research about spiders. He then succeeded in making a synthetic spider webbing with amazing adhesive ability. Not wanting anyone else to know about his powers. Komori sewed a costume and took up the identity of Spider-Man.