Gradius (1986) is one of the founding fathers of the side-scrolling shoot-'em-up, and its great innovation was the power-up bar along the bottom: collect capsules, watch the selector march across Speed, Missile, Double, Laser, Option, and cash in when you reach the upgrade you want.

That choice — do I grab speed now or save for an Option drone? — turned a shooter into a strategy game. The Moai (Easter Island head) stage and the relentless difficulty became legend.

And yes: the famous Konami Code (up, up, down, down…) became a household phrase largely because Gradius players needed those extra power-ups to survive. A genre cornerstone.