Watch cliff divers, bungee jumpers, or even just kids fooling around and jumping into a lake. At some point, one or more of them will yell "Geronimo!" It's a safe bet that at some point, we've all yelled this name.
It seems like a pretty random thing to yell when jumping from a bridge, cliff, or plane, but it's actually from the military tradition of paratroopers yelling it as they jumped from a perfectly good airplane.
But where did the paratroopers come up with it?
It dates all the way back to the origin of paratroopers. In 1940, the Army was still developing the strategy of dropping troops out of planes. On the eve of the first test jump, soldiers from from Fort Benning started a night of drinking with a viewing of a wild west movie beforehand. This was likely the 1939 film "Geronimo" starring Andy Devine and Chief Thundercloud.
After the movie, Pvt. Aubrey Eberhardt boasted that he wasn't scared of the jump, despite being the tallest man in the unit. This caused his fellow soldiers to call him out on his bragging, saying he would forget his name at the door, as the troops were supposed to shout their name when they jumped.
Everyone in their jump group successfully jumped — all the soldiers remembered their names and shouted them as they made their jumps.
The 6'8" Eberhardt did them one better — when his turn at the door came, he shouted "Geronimo!" — and a new military tradition was born.
Some of the top military brass weren't in love with the new tradition, but others thought it evoked the bravery and daring of the Apache chief — the last holdout against American expansion to the West. They let the paratroopers keep the tradition.
Civilians just kinda took it from the paratroopers. And who could blame them, with that kind of pedigree?