Whiskey In The Jar is as ould as tae, as we say round these parts. It's a mash of an even older song about a highwayman called Patrick Fleming, the melody comes from a reel that's probably even older than that (I found it in a book of fiddle music from 1860, for one thing). There's a few hundred variants of it as well, as befits this kind of thing.
The one that annoys me is "I Put A Spell On You". Telling people that's not a Nina Simone original has led to proper stand-up arguments.