Artworks that explore sexual identiy may include the experiences, sociopolitical struggles, and ideas associated with gay, lesbian, bisexual, and transgender identities. While homosexuality was embraced in Classical Greece, as evident in the era’s philosophy and artwork, throughout most of history it has been rejected and persecuted. Artworks that explore non-heterosexual identities have consequently often done so implicitly, such as Marsden Hartley's Portrait of a German Officer, in which the artist depicts his lover using abstract insignia. Later, subtle references to homosexuality appeared in the works of Jasper Johns and Robert Rauschenberg—who were lovers and collaborators—and the gay icon Andy Warhol developed a signature camp aesthetic. With the arrival of the AIDS crisis in the 1970s and ‘80s, numerous members of the art community lost their lives, and homosexuality became an overt, politicized theme; Nan Goldin, Felix Gonzalez-Torres, Keith Haring, and David Wojnarowiczfound unique means of expressing the tragedies and struggles of this period. While political activism is still a central practice among many queer artists, others have addressed these issues in terms of theory or self-identity.