Partially inspired by this uhoh question on SciFi.SE
In writing up my answer, I came across this interview Clarke gave to NPR in 2008 where this quote is made
While Clarke came up with the idea of the communications satellite, it was John Pierce of Bell Labs who was instrumental in developing the first communications satellites, Echo I and Telstar, in the 1950s. Clarke had interacted with Pierce during that period.
Das: Do you consider the paper on geostationary orbits your most important contribution?
Clarke: It’s definitely my most important contribution. And maybe in a generation or so the space elevator will be considered equally important.
The article implies Clarke played some important role but never focuses on that role enough to paint a complete picture. How much of a role did Clarke's ideas play in helping to make modern satellites what they are today?