Simple question: What is the Universe really made of? Yet, not-so-simple answer: Mostly stuff we can’t see! Join me on an astronomical journey into the mysterious world of “dark matter,” where we will explore how we use gamma rays—the most energetic bursts of light—to hunt for clues of dark matter. In this talk, I will outline the path from early gamma-ray astrophysical observations to today’s most sensitive gamma-ray missions, like the Fermi Gamma-ray Space Telescope, and look ahead to the next big leap: the Cherenkov Telescope Array. Along the way, we will encounter exotic particles like axions or WIMPs that could help us finally unlock the nature of the Universe.