Gradius (1985 in arcades, 1986 on the NES) is one of the founding fathers of the side-scrolling shooter, and its great innovation was the power-up bar along the bottom. Collect a capsule and a selector marches one step across Speed, Missile, Double, Laser, Option and Shield. Cash in whenever you like, and the selector resets to the start.

That single mechanic turns a shooter into a resource game. Do you spend at Speed now, because you're getting cornered, or bank four more capsules for an Option drone that will double your firepower for the rest of the level? Options are the obvious prize and the reason to be patient: each one is a floating orb that traces your exact path a moment behind you and fires everything you fire. Four of them and the screen belongs to you.

The flip side is the death spiral, and Gradius invented that too. Die and you lose the lot, respawning naked in a section balanced for a fully loaded ship, usually at the slowest speed setting with enemies already on top of you. Recovery is its own skill. Experienced players will deliberately hold Speed at two rather than three, because a ship that moves too fast is harder to thread through the tighter corridors.

The Moai heads spitting rings, the fortress full of rotating walls, and Vic Viper's whole silhouette became shorthand for the genre.

The NES port is also where the Konami Code entered the world. Kazuhisa Hashimoto was doing the conversion, found the game too hard to test properly, and put in up, up, down, down, left, right, left, right, B, A to hand himself a full loadout. He forgot to take it out. It has been in Konami games, and a fair number of other people's websites, ever since.

A genre cornerstone, and still a good argument that a shooter can be about decisions rather than reflexes.