Steve Reeves, Reg Park (in the 40's, he was on in the 60's and 70's no doubt there), George Eifferman, etc. Those guys were as big as it gets natural. You have to remember they were fairly lean and not only were roids unheard of when they built their mass (late 30's and 40's) but there were no supplements either. No creatine, no 100 different choices of whey, no fat burners, crude equipment, no pump enhancers. Just hard work and as much good solid food they could eat.
As for todays guys, it's hard to tell. You never know who's lying. And even if they pass a drug test there's always slin, igf1, hgh, etc. Not to mention the legal supplements and equipment we have availible today.