Along the lines of the recent thread about the most underrated ballplayers out there, I'd like to put forth Tony Iommi as one of the greatest, and most underrated, guitarists of all time. Arguably the Father, Grandfather, and Godfather of heavy metal, all rolled into one. He is the Mordecai Brown of rock guitarists, to tie things into our beloved hobby.
Quite honestly, with no Iommi, there likely would have never been an Ozzy Osbourne as we came to know him.
Fairies Wear Boots - Entire song, but especially starting at 2:40
Paranoid - 1:27
Turn Up the Night - 1:50 (Not that great of a song IMO, but they stuck it in this online article for some reason.)
Snowblind - 2:35 - 3:40 - and especially 4:40
Iron Man - 3:10 and again starting at about 4:40
War Pigs - 3:25 and then especially stating at about 5:26 through the end of the song
https://faroutmagazine.co.uk/tony-io...-guitar-solos/
And their entire debut album, titled Black Sabbath, is unreal and probably their most, and one of all of rock-n-roll's, most underrated albums of all-time. The rain, haunting church bells, and opening chords of the album's first and titular song, Black Sabbath, is to my thinking one of the greatest opening songs to ever launch an album and a band, and immediately let everyone know what they were all about. There really hadn't been anything like this before them. And if you like bass guitarists, listen to Geezer Butler on Bassically starting at about the 14:20 mark, which then rolls into N.I.B., one of Sabbath's best songs that no one really seems to know or ever talk about. At the 23:50 mark it goes into Sleeping Village/A Bit if Finger, which is well worth a listen. And then at 27:40 it morphs into the final song/movement of the album, Warning. You especially want to start listening to it at the 31:00 mark when Iommi takes over and it is basically his solo effort through the next 7 minutes to end the approximately 38 minute long album. Throughout the entire album you hear Iommi playing various styles and influences that aren't necessarily what you'd expect from a straight up, heavy metal, rock band. With the different styles and techniques used, I've always felt this album was more in line with, and deserved to be right up there with, the likes of the Beatles - Sgt. Peppers and the Beach Boys - Pet Sounds albums.
https://www.youtube.com/watch?v=YztzNyDGcpc
And some honorable mentions I haven't heard brought up yet, Frank Zappa and Robert Fripp. I don't think any explanation is needed for either of them.