Fritz Klein is very important to me because he invented the Klein Sexual Orientation Grid, which expands upon the more traditional Kinsey Scale by, among other things, acknowledging that people's sexual orientations can change over time.
(Please note that Alfred Kinsey himself did not believe sexual orientations were inherently fixed or unchanging either - Kinsey only intended his scale to measure people's past sexual experiences, not to imply that their orientations were eternally fixed. The Klein Sexual Orientation Grid goes beyond the Kinsey Scale, however, by explicitly attempting to measure the changes in people's sexual orientations over time. It assigns Kinsey ratings to people's past, present, and "ideal" orientations in various categories including sexual attraction, sexual behavior, and sexual identity.)
Fritz Klein died of a heart attack on May 24th. He was 73 years old.
Thank you, Fritz Klein.