Some songs are so iconic that it's impossible to imagine someone else improving upon them. They're so personal and specific to that artist, the very idea of another musician trying their hand at it seems laughable. But then every so often that fresh take exceeds expectations and outshines the original by a mile. So much so that people forget that it's a cover song at all.
Johnny Cash didn't write "Hurt," for example, but many people reading this article right now have never heard the original version by Nine-Inch Nails. Because Cash took the song to a whole new level. But then, that's the beauty of a truly original cover song, if such a thing exists.
For another artist to rewrite someone else's work and take it to such heights of creativity and/or popularity that it completely overshadows the source material is not only rare, but almost heroic. Any musician trying to re-do someone else's work is begging to hear choruses of music snobs groaning about its inferiority while pleading with the music industry to stop digging up and mangling the past. And yet some artists prevail in that most unexpected of ways, achieving god-like status for turning what was once just a great song into a quintessential song.
Of course, other musicians can simply pluck a random song from obscurity that no one knew about in the first place and do a decent enough job with it gets them on the radio, and without all that ugly idealism. Popular music isn't always about grandeur, after all.
These are the cover versions that not only popularized a lesser known track, but revamped them into something brand new and, often, something more palatable...