Guitar duos are still the thing, man. Ain’t nothing better than to listen to two cats play off one another: John and George, Hammett and Hetfield, Allman and Betts, Trucks and Haynes, Ronnie and Keef, Jimmy Page and himself …
But go way back to 1959, and have a listen to John Lee Hooker and (I think*) Eddie Taylor jam their way through I’m In The Mood.
* I know there are multiple versions of this track. They’re all terrific, but hopefully I’m referencing the right one.