I'm sure by now they have all been mentioned but ....
Robert Johnson, BBKing, Albert King, Howlin Wolf and Muddy Waters to start the core but there are so many more in that league...Albert Collins, Paul Butterfield Blues band, John Lee H**ker.... As far as later bands: Allman Brothers, Stevie Ray Vaughn, John Mayall BLuesbreakers (the early lps), Derek and the Dominoes , Rory Gallagher,,,etc...many more.
Personally I prefer the white British blues & blues/rock guitar players and bands from the late 1960s such as Cream featuring Eric Clapton, Taste featuring Rory Gallagher, Ten Years After featuring Alvin Lee, Savoy Brown featuring Kim Simmonds, Chicken Shack featuring Stan Webb along with Peter Green's Fleetwood Mac and The Groundhogs featuring Tony McPhee and Free featuring Paul Kossoff and with regards to American blues and blues/rock guitar players mainly Johnny Winter and his 'rock period' between 1970-1975 and Michael Bloomfield Chicago type blues guitar style.
Well, if you want to start at the beginning, start with Robert Johnson. (that's just my opinion)
However, I can only tell you how I got into it.
I stumbled upon Stevie Ray Vaughan, and from there, the show was on. It was instant love. Lol. I spent the next couple years getting all his stuff, combing the buy and sells for bootlegs, etc. Couldn't get enough.
SRV opened up a whole new world for me. I spent a couple years darting off in different directions within the blues genre, discovering long standing artists I'd always heard of, known about, but never bothered to listen to because it was the 'blues'.
But, I always come home to roost with my boy SRV. He's tops for me.
Yeah SRV up to a point but I never much cared for his 'clean guitar tone' on all of his studio and live recordings it's not biting enough for me and his vocals are a bit dead or flat sounding in my humble opinion but I do still have all his studio albums and I like Texas Flood from 1983 especially.