On this day in 1973, Samantha Mulder mysteriously disappeared from her home while playing a game of Stratego with her brother Fox. He was convinced that she was taken by aliens, sparking a lifelong quest to get to the truth behind the abduction. Whether he ever truly got to the bottom of the mystery is up for debate.

To celebrate: Run a marathon of X-Files mythology episodes, and tyr to figure out for yourself exactly what happened to Samantha Mulder.

(The X-Files, TV series, 1993-2016)