The history of free-flying occulters to search for extrasolar planets goes back to at least the early 1960s. Robert Danielson of Princeton suggested the notion to Lyman Spitzer who published a short analysis of the idea in "The Beginnings and Future of Space Astronomy" in American Scientist in 1962. Lyman Spitzer is known in some circles as the father of space telescopes and was instrumental in the development of the Hubble Space Telescope.
Less than a dozen years later, the next significant step in analysis of the idea came with Gordon R. Woodcock, then a study manager at Boeing. Woodcock validated Spitzer's analysis, extended it, and then suggested a plausible design for implementing the idea. This work was largely unknown until recently as it was included as an appendix to a NASA contractor report on Future Space Transportation Systems.
In the early 1980s, Christian Marchal, of ONERA investigated shapes of occulting screens which are neither disks nor rectangles. He found that the ability of a screen to suppress light from a star can be enhanced by choosing complex shapes.
Many have studied how to use extra-focal-plane occultation techniques since Spitzer and Danielson, however, the idea has not seemed practical until recently. In the mid/late-1990s, a group at Case Western Reserve and JPL, led by Glenn Starkman and Craig Copi have suggested a very large, light-weight apodizing screen to perform occultation work either in conjunction with ground based observatories or with space telescopes. Copi & Starkman call their occulter idea BOSS.
Jean Schneider, webmaster at the Observatoire de Paris and keeper of the Extrasolar Planets Encyclopaedia has also done some analysis on free-flying occulters.
TRW, Boeing SVS, and other companies have even considered occulters as precursor missions to the Terrestrial Planet Finder.
