Kenneth Earl Wilber II (born January 31, 1949) is an American theorist and writer on transpersonal psychology and his own integral theory, a four-quadrant grid which purports to encompass all human knowledge and experience. Starting publishing in the 1970s, his works were popular among a section of readers in the 1980s, but have lost popularity since the 1990s, retaining some popularity at dedicated web forums. Source: Wikipedia (en)