Nergal based on Slender Man?

Hey guys this ain't mine I found it on Tumblr and I just had to share it.
So anyway I've read that Nergal from The Grim Adventures of Billy and Mandy is based on Slender Man I mean the show came around before we all knew about Slender Man.
But I also read that the legend of Slender Man is older then The Grim Adventures of Billy and Mandy.
They do look alike don't they?
Slender Man also kinda looks like Jack Skellington from Nightmare Before Christmas.
But maybe when Maxwell Addams came up for the idea of Nergal somebody told him the legend about Slender Man
Before we all knew about it.
I mean we already knew that Grim was based on The Grim Reaper and Boogey was based on The Boogeyman right?

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