As far as I can see, Bernard Hopkins was ranked for 24 consecutive years by ring magazine from 1991-2014. Has any other fighter we can think of ever been ranked that long or at the very least by Ring? it should also be noted that he has claim to a combined 7 years of "lineage" between his middle and light heavy reigns. I didn't bother to count the number of years where he was a belt holder of one kind or another but I'm sure its crazy..
It must be a record. Consecutive OR non-consecutive I can't imagine any fighter featuring in 24 years. Not Robinson, Duran or Moore. To put in perspective, Cassius Clay/Muhammad Ali was only ranked in 18 years, 1961 to 1978, and that's including 1968 and 1969 when RING magazine recognized him as champion during his legal troubles over the draft and forced inactivity. Evander Holyfield, (who fought for 27 years), was only ranked 17 years by RING, from 1985 to 2002, excluding 1994 where he was assumed retired for health reasons. Floyd Mayweather Jr, clocked up 16 years rated, 1998 to 2014, exluding 2008 when he was 'retired'. Wladimir Klitschko has only been rated in 14 years, virtually guaranteed to be 15, from 2000 to 2015, exluding 2004.
Looking at some numbers, Hopkins has been ranked for roughly 16% of the existence of Queensbury rules since their being put into regulation in 1867... Unbelievable.