When was kryptonite invented?

Kryptonite was created for The Adventures of Superman radio serial in 1943 and first appeared in comics in Superman #61 in 1949.

Why does kryptonite hurt Superman?

In DC continuity, kryptonite is irradiated debris from the destroyed planet Krypton, and its radiation poisons Kryptonian physiology, stripping Superman's powers and eventually killing him.

What do the different kryptonite colours do?

Green kryptonite weakens and can kill Kryptonians, red causes unpredictable changes, and gold has been used in stories to remove Kryptonian powers permanently. The colours were added over decades to create new plots.

Is kryptonite Superman's only weakness?

No. Magic is his other long-standing vulnerability, and in most eras his powers are fuelled by yellow sunlight, so prolonged absence of it weakens him too.

Why Kryptonite Is Superman's Weakness (It Started on Radio)

A hero who cannot be hurt is a hero with no stories. Kryptonite exists to solve that problem — and it was invented for radio, not for the page.

Here is where it actually came from, when it reached the comics, and why the colour-coded varieties turned up later.

It was invented for The Adventures of Superman radio show

The radio serial The Adventures of Superman introduced kryptonite in 1943, as a piece of Superman's exploded home world that could weaken him. The practical benefit was immediate: a nearly invulnerable lead can be threatened, captured and left in peril at the end of an episode.

A widely repeated bit of production lore is that it also let the show run without its lead actor for stretches — Superman groaning under kryptonite could be voiced by anyone. Treat that as show-business anecdote rather than documented fact.

FactKryptonite was introduced on the Adventures of Superman radio serial in 1943, before appearing in the comics.Source: Encyclopaedia Britannica

The comics adopted it in 1949

Kryptonite reached DC's comics in Superman #61 (1949), the story that also established Krypton as Superman's home planet in continuity. From that point it became the single most reliable plot device in the character's history.

Writers later expanded it into a colour system — green weakens, red causes unpredictable transformations, gold was used to strip powers — largely as a way to keep generating new stories from the same rock.

FactKryptonite first appeared in DC's comics in Superman #61, published in 1949.Source: DC

Why it still works as storytelling

Kryptonite is a good weakness because it is external, visible and portable. Lex Luthor can carry it in a lead box; a reader can see the danger on the page. Compare that with Superman's other classic vulnerability — magic — which is abstract and hard to draw.

It also keeps the character human. Superman is interesting when he chooses to keep going while hurt, and kryptonite is the simplest way to put that choice in front of him.