The Brookings Institution

The Brookings Institution, whose predecessor was founded in 1918 by Robert Brookings, was probably the first think tank in the USA.

Enjoying close ties with Rockerfeller and Carnegie, Brookings played an important role in the emergence of the political-lobbyist strand of philanthropy which funds much of the right-wing think-thank ecosystem today.

Sources:
Sourcewatch

Related:
Brookings - The Establishment's Think Tank
Schlepping to Moguldom" (This article is also available here.
IRmep, The Brookings Saban Center- Errors of Ommission