A very long time ago (15 years maybe?) there was a great internet site (I don't remember the name anymore) which showed a graph of top ~100 largest companies in the USA, their CEOs and their boards.
When expanding the graph you could basically see that the same 30 or 40 people where in the boards of major companies, from Pepi to Johnson&Johnson to Microsoft to Fox and other communication companies.
It showed a really interesting picture of how really consolidated the control was at the top.