As in physical In ring strength. Honorable mentions: Briggs K's Rahman SNV Lennox Peter Ustinov Chisora Larsen Foreman McCline P4P Froch Lamotta Ward Canelo Lacy Golovkin Mosley Broner (130)
Rahman and Sugar Shane were both known for their incredible strength when it came to weight lifting, but that doesn't always translate in the ring. Pound for pound Dick Tiger might be the strongest. The ease with which he was able to bully Gene Fullmer and Hurricaine Carter around (who were both known for his crazy strength) is still surprising.
All-time "STRONG" fighters Heavyweights: George Foreman Mike Tyson Evander Holyfield Middleweights: Marvin Hagler Carlos Monzon Roy Jones Jr. Lightweights: Julio Caesar Chavez Roberto Duran Kostya
I'd say Wladimir Klitschko, for the amount of oxygen he is able to burn, thus the overall strenght he's able to generate.
Broner is strong in the ring against limited opposition, and that he has functional strength, but his bench press video indicates he isn't really that strong pound for pound in a weight lifting sense. Rahman used to rep like 500 pounds on bench at the gym I used to go to - he is the strongest person I have ever seen live. Of course, there are different kinds of strength, and I reckon you aren't talking about static strength entirely but something more like functional strength. So there isn't really a correlation between in ring and weight lifting ... but there are some very strong guys who don't necessarily hit hard, but who can move people around and not be pushed back.