Zac Vawter is a 31-year old software engineer who tragically lost his left leg after a motorcycle accident. Like most amputees, he was outfitted with a typical prosthetic leg that helped him get around. It wasn’t until he became a research subject at the Rehabilitation Institute of Chicago that he’d become a genuine bionic man set to make history on Sunday by climbing to the top of Chicago’s Willis Tower, one of the world’s tallest skyscrapers.