Artificial selection and mutation have made this incredibly fast human who uses his speed for heroics.
Although natural selection and time has created his arch rival who is incredibly strong with a high fitness his name is the bulk.
SInce the bulk does not have a low birth rate he has a lot of offspring and all of his children inherited his bulkiness
While the speedster was out saving people the bulk was trying to convice his chihldren to help him but some of his children wanted to use their strength for good
The Bulk Took his chid that was mean and went to defeat the speedster but he was to quick. he ignored the child and caught the bulk off guard. He then decided to talk to the Bulk and turn him good
They became friends for life and talked about all the epic battles they had and also the epic adventures they had. but eventually they got old and died. Their offspring passed on thier genes and kept the heroics going.