From where I sit I count at least 3 Eric Claptons.
The first, in the 1960s was this chap ...
… who hung in there through the groups Cream, Blind Faith and Delaney & Bonnie up to 1970.
Then, in 1970 we get the first impostor, Derek, as in Derek and the Dominos.
I think it's very telling that a different name was chosen for #2 since it wasn't really Eric anymore (like The Beatles using “Sgt Pepper” when it wasn't the original band anymore).
Eric #1 has round face, weak chin, dark hair. Derek has reddish brown hair, longer face, stronger chin. Their voices and accents are also different. Their on-stage manner is also different. Eric is very laid back, almost shy while Derek is more forceful.
Derek didn't last long and disappeared for about 3 years at about this point. We're told it was due to drug addiction.
Then, about 1974 “Eric Clapton” returns but his album (“461 Ocean Blvd”) has no photo of him and when he appears in public he's wearing a full beard which he keeps for about 10 years making an ID difficult but I believe that Eric #3 (under the beard) is this guy, shown here about 1985 after finally losing the facial hair:
I don't think #3 looks anything like Eric or Derek but maybe that's just me.
Since 1974 “Eric” is now a solo artist and sings lead vocals on most of his songs while the first Eric did not like being a “front man” or singing leads and rarely did so. I suspect that is why he was replaced since they wanted a full fledged rock star and the real Eric “just wanted to play in a band” as he put it.
Now, I could be wrong about some of this and there might have been more than 3 of them but these are the ones I feel pretty sure about at this point. It's difficult to research Clapton because there is a lot of photo fakery on "Eric Clapton," both on individual photos and on album covers plus the facial hair problem.
Charlie Chaplin once entered a Charlie Chaplin lookalike contest and lost.