Aside from Charlie Whiting, the FIA Race Director, the race stewards who look at and deliberate on on-track incidents are apparently not the same every weekend.
There have been races where I hear the Sky F1 commentators mention a few familiar names as part of the stewarding team, former F1 drivers like Emanuele Pirro and Nigel Mansell.
Looking around the internet, the FIA website has published biographies for known race stewards of certain race events, but they all come from different backgrounds in the motorsport industry, some of them former FIA officials and some racing drivers. (see source)
Is there any specific criteria for selecting race stewards? Does being a former F1 driver qualify you to be one? And did these people volunteer or are they a part of a collection of people that are assigned to be race stewards every race weekend?
Sources (via FIA website):