His design is actually based on the Fiat Trepiuno concept, which was penned by Roberto Giolito. But Stephenson added many of the key styling cues that made the Fiat 500 popular and explained the entire process by putting together a couple of sketches on a piece of paper.
If you’re not familiar with Stephenson’s work, the Fiat 500 is just one of many iconic cars he designed. He started out by designing the large double spoiler of the Ford Escort RS Cosworth before moving to BMW, where he penned the Mini Cooper, also a revival of a beloved classic. He also designed the first-generation BMW X5 before he was appointed director of Ferrari-Maserati Concept Design and Development. During this time, his team created the Maserati GranSport and MC12, and the Ferrari F430 and FXX. Following his tenure at Fiat, Stephenson became the Design Director of McLaren Automotive, where he oversaw the design of the MP4-12C, P1, 570S, 675LT, and 720S.