Oncen Enderman who loved everything crimson (even if those things were pure evil) was killed by a player. Even when the Ender Dragon avenged the Enderman, it couldn't reert this loss. But the Crimson Hive from neighboring universum could. Now Crimson Endermen (yes, Crimson Hive developed a "taste" in assimilating Endermen) search for every single human across ALL universes, to kill and assimillate them, just like everything else.
Previously, like other variations, it was just a recolored Enderman. Now it looks more natural. And yes, the "Crimson" idea came from Terraria, it's even in the lore.
(Skin and lore remade by Ender Sparkle)
(Original lore suggestion by thewatcherofstreas)