For more than three decades, gamma-ray bursts have grown from an oddity to a central topic in astrophysics. Not only are they the largest explosions since the big bang, capable of flooding most of the universe with gamma-rays, but their brilliance serves as a backlight that can illuminate the cosmos far deeper into the early universe than any other object. Their unpredictability has forced researchers to use extreme measures to observe them: completely autonomous satellites and robotic ground-based telescopes. Their bizarre physical properties have required new theories on massive explosions.