Complex sentence: In doing so, he followed in the footsteps of Terry Fox; unlike Fox, who had to abandon the Marathon of Hope when his cancer returned, Fonyo completed the coast-to-coast marathon and also completed a marathon across the United Kingdom.
Split into simpler sentences: In doing so, he followed in the footsteps of Terry Fox. Unlike Fox, who had to abandon the Marathon of Hope when his cancer returned, Fonyo completed the coast-to-coast marathon and also completed a marathon across the United Kingdom.