Think tanks are research organizations typically focusing on specific topics, generally set up as nonprofits with tax-exempt status. They go back at least to the 19th century. The Institute for Defense and Security Studies was founded in London in 1831. Or they could go back to Charlemagne about 800 to maintain his Holy Roman Empire (which was not Roman, not an empire, and certainly not holy). Andrew Carnegie founded the first American Think Tank in 1910, the Carnegie Endowment for International Peace--just four year before World War I.
Currently there are thousands of these and they seem to pop up like mushrooms whenever some rich guys have an ax to grind. The ones of interest are political/governmental and economic. They can be non-partisan and generate research that is fact-based and non-ideological. Or totally partisan and rely on "facts/findings" that support their positions. Upsetting Daddy Bigbucks is a definite job killer.