When you think 'chess ratings', you probably think about Arpad Elo, the father of the FIDE rating system. When you think 'Elo', you might also think about chess titles, because Elo's rating system had a profound impact on the awarding of titles.
I added Elo's own summary of early title regulations to my page on FIDE Titles (see Fischer's IM/GM Titles for the previous post about that page). Then I extracted the following chart from the same source.
Elo, 'The Rating of Chess Players Past and Present', p.69
It shows the evolution of FIDE's title and rating systems from 1950, when the first titles were awarded, to 1977, when Elo's book (Batsford 1978) was under preparation. For another look at Elo's work in the context of titles, see my 2008 post Titled Players, Sizing the Data.