(TW: used of the q-word throughout this page, as a reclamation)
"Queer is by definition whatever is at odds with the normal, the legitimate, the dominant. There is nothing in particular to which it necessarily refers. It is an identity without an essence. 'Queer' then, demarcates not a positivity but a positionality vis-à-vis the normative." 
"Queer theory developed out of an examination of perceived limitations in the traditional identity politics of recognition and self-identity. [...]
In particular, queer theorists identified processes of consolidation or stabilization around some other identity labels (e.g. gay and lesbian); and construed queerness so as to resist this. Queer theory attempts to maintain a critique more than define a specific identity.
Acknowledging the inevitable violence of identity politics, and having no stake in its own ideology, queer is less an identity than a critique of identity. However, it is in no position to imagine itself outside the circuit of problems energized by identity politics."
Queer vs Gay
"Gayness and queerness are two different things, but sometimes gayness is a part of queerness and vice-versa."
(see also ACT UP)
"Queer theory was originally associated with radical gay politics of ACT UP, OutRage! and other groups which embraced "queer" as an identity label that pointed to a separatist, non-assimilationist politics."
Queer theory was largely developed in response to increasing normalisation of gay and lesbian identities, prompting a divide between those who desired assimilation (where possible) and those who, more radically, wanted to eradicate the heteronormative structures that oppress queer people.
"In America since the mid 90s a fierce debate has raged between assimilationist lesbians and gay men and radical queers. The assimilationists want gay marriage, inclusion in the military, the right to adopt children–i.e., equal status within the status quo. Queers, on the other hand, want nothing to do with the status quo, instead regarding the most vibrant and radical aspect of homosexuality as being precisely its opposition to normative sexuality and society."
Karl Heinrich Ulrichs
- "Karl Heinrich Ulrichs (28 August 1825 – 14 July 1895) was a German writer who is seen today as a pioneer of the modern gay rights movement."
The use of the word queer has been contested as a slur, will do more research on its history when I can.
For now, I just noticed that William S. Burroughs was already using it in a reclaimed sense as early as 1959 in his novel "Naked Lunch" (page 16) in a conversation between Lee and Allerton:
Lee: "Solid, Pops.... So how was your evening with Dumé?"
Allerton: "We went to several bars full of queers. One place a character asked me to dance and propositioned me."
Lee: "Take him up?"
(actually that's not so reclaimed, because it's Lee who is homosexual and even Lee partially detests his own queerness)
Marilyn Monroe and James Dean were two of the first super-celebrities of the Pop culture era. Both died young, and both were non-heterosexual ("queer" in the indirect sense of being non-cishet).
- David Halperin (1997-02-06), "Saint Foucault: Towards a Gay Hagiography", Sexualities, Oxford University Press, 13 (3): 62, ISBN 0-19-511127-3, retrieved 2010-05-10
- Blackburn, S 1996, "essentialism", Oxford Dictionary of Philosophy, (Oxford Reference Online).
- "Queer Present, Queer Past, Queer Future" http://www.academia.edu/1061762/Queer_Past_Queer_Present_Queer_Future