Brent Stirton is driven by a passion to help others. Whether photographing sex workers in Ukraine or rangers on the front lines of the fight against illegal wildlife poaching, Stirton uses his photographic gift to tell these stories in a way that makes us take notice. We spoke with Stirton for our new series “Through the Lens,” where we get to know the photographers behind the unforgettable images showcased on National Geographic.

The first picture that mattered to me was probably shot in 1994 during the run-up to the first democratic South African election. I had been shooting images for less than six months at that stage. I remember I was in a crowd that was quite agitated—a police dog bit