Richard Colestock Pillard (born 11 October 1933) is a professor of psychiatry at the Boston University School of Medicine best known for his work on biology and sexual orientation.
Pillard says that it had long puzzled him why transsexuals—men or women who wish to live in bodies of the opposite sex—are so different from gay people: “You’d think they’d be on the far end of the spectrum, the ‘gayest of the gay.'” And yet transsexuals are not in fact gay. Whereas gay men, quite comfortably and unalterably, see themselves as men, male transsexuals see themselves as women trapped in men’s bodies. Pillard and a colleague, James Weinrich, a psychobiologist at the University of California at San Diego, began to theorize that gay men are men who in the womb went through only a partial form of sexual and psychosexual differentiation. More precisely, Pillard and Weinrich theorized that although gay men do undergo masculinization—they are, after all, fully male physically—they go incompletely if at all through another part of the process: defeminization.
It is this process of defeminization that is the central concept in an overarching model of gender transposition stated by Pillard and coauthor James Weinrich. It contains elements of John Money’s neurodevelopmental model. 
Pillard was born in Springfield, Ohio. He briefly attended Swarthmore College before transferring to Antioch College, where his father Basil H. Pillard was an English Professor. Pillard received his B.A. from Antioch.  He then earned his M.D. from University of Rochester, with his internship at Boston City Hospital.
Pillard married Vassar graduate Cornelia Livingston Cromwell in 1958, while he was in medical school. They later divorced when he was in his thirties, and Pillard now identifies as gay. He has three daughters. The oldest daughter, Vicky Pillard, is a pediatrician practicing in Amherst, MA. His second daughter, Nina Pillard, is a Georgetown University Law Center professor and was formerly assistant to Attorney General Reno. His youngest daughter, Eliza Pillard, is a social worker specializing in child psychiatric issues in Vermont.
Chandler Burr reported that Pillard jokes “he is uniquely equipped to investigate whether homosexuality has a biological basis: he, his brother, and his sister are gay, and Pillard believes that his father may have been gay. One of Pillard’s three daughters from a marriage early in life is bisexual. This family history seems to invite a biological explanation, and it made Pillard start thinking about the origins of sexual orientation.” 
Heritability of sexual orientation
Pillard is well-known for a series of studies he coauthored with J. Michael Bailey, which examined the rate of concordance of sexual identity among monozygotic twins, dizygotic twins of the same sex, non-twin siblings of the same sex, and adoptive siblings of the same sex. In all studies they found rates of concordance variantly consistent with the hypothesis that homosexuality has a significant genetic component. The Council for Responsible Genetics and other researchers have criticized this work for using a self-selected sample, a problem which later studies have attempted to remedy.
Pillard feels that some of his most significant work deals with the incidence of homosexuality running in families.
* Pillard RC, Rose RM, Sherwood M. Plasma testosterone levels in homosexual men. Arch Sex Behav. 1974 Sep;3(5):453-8. PMID 4415098
* Pillard RC, Weinrich JD (1987). The periodic table model of gender transpositions, part 1: a theory based on masculinization and defeminization of the brain. The Journal of Sex Research Vol. 23, No. 4, pp. 425-454.
* Bailey JM, Pillard RC. A genetic study of male sexual orientation. Arch Gen Psychiatry. 1991 Dec;48(12):1089-96. PMID 1845227
* Tuttle GE, Pillard RC. Sexual orientation and cognitive abilities. Arch Sex Behav. 1991 Jun;20(3):307-18. PMID 2059149
* Pillard RC, Weinrich JD. Evidence of familial nature of male homosexuality. Arch Gen Psychiatry. 1986 Aug;43(8):808-12. PMID 3729676
* Pillard RC, Poumadere J, Carretta RA. A family study of sexual orientation. Arch Sex Behav. 1982 Dec;11(6):511-20. PMID 6760832
* Pillard RC, Poumadere J, Carretta RA. Is homosexuality familial? A review, some data, and a suggestion. Arch Sex Behav. 1981 Oct;10(5):465-75. PMID 7032464
* Dawood K, Pillard RC, Horvath C, Revelle W, Bailey JM. Familial aspects of male homosexuality. Arch Sex Behav. 2000 Apr;29(2):155-63. PMID 10842723
* Bailey JM, Pillard RC, Dawood K, Miller MB, Farrer LA, Trivedi S, Murphy RL. A family history study of male sexual orientation using three independent samples. Behav Genet. 1999 Mar;29(2):79-86. PMID 10405456
* Pillard RC, Bailey JM. Human sexual orientation has a heritable component. Hum Biol. 1998 Apr;70(2):347-65. PMID 9549243
* Pillard RC, Bailey JM. A biologic perspective on sexual orientation. Psychiatr Clin North Am. 1995 Mar;18(1):71-84. PMID 7761309
* Snyder PJ, Weinrich JD, Pillard RC. Personality and lipid level differences associated with homosexual and bisexual identity in men. Arch Sex Behav. 1994 Aug;23(4):433-51. PMID 7993184
* Pillard RC, Rosen LR, Meyer-Bahlburg H, Weinrich JD, Feldman JF, Gruen R, Ehrhardt AA. Psychopathology and social functioning in men prenatally exposed to diethylstilbestrol (DES). Psychosom Med. 1993 Nov-Dec;55(6):485-91. PMID 8310108
* Weinrich JD, Snyder PJ, Pillard RC, Grant I, Jacobson DL, Robinson SR, McCutchan JA. A factor analysis of the Klein sexual orientation grid in two disparate samples. Arch Sex Behav. 1993 Apr;22(2):157-68. PMID 8476335
* Bailey JM, Pillard RC, Neale MC, Agyei Y. Heritable factors influence sexual orientation in women. Arch Gen Psychiatry. 1993 Mar;50(3):217-23. PMID 8439243
1. Burr, Chandler (June 1997). Homosexuality and biology: the puzzes of chemistry. The Atlantic Monthly
2. Debor, Holly FTM: Female-to-Male Transsexuals in Society
3. Judson, Jerome (March 1958). Departure: Basil Pillard, 1895-1957. College English, Vol. 19, No. 6, Poetry and Professors Issue , p. 240
4. Paul E. Lynch (2003). An Interview with Richard C. Pillard, MD. Journal of Gay & Lesbian Psychotherapy Volume: 7 Issue: