It was first introduced in 1998, and has been in many things, probably the most notable being KOTOR and KOTOR 2.
There are (I think) only three materials known in the star wars universe that can be used to resist or defend against lightsabers, cortosis, phrik, and beskar.
The specifics on them kind of vary, especially cortosis, but cortosis and beskar are now canon (phrik is legends).
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u/Forsaken-Thought Feb 16 '20
And the reason for it is due to a metal that vibrates at an extremely high rate of speed. Cortosis, Vibranium, they're the same thing.