sex symbol is a famous person or fictional character widely regarded to be very sexually attractive. 
sex symbol was first used in the mid-1950s in relation to the popularity of certain film stars and pin-up models, including Marilyn Monroe, Brigitte Bardot, and Raquel Welch. This concept was a reflection of the post-  World War II increase of sexual and economic emancipation of women. 
In the 20th century, sex symbols could be male as well as female: actors such as the romantic
Sessue Hayakawa and the athletic Douglas Fairbanks were popular in the 1910s and 1920s. Archetypal screen lover Rudolph Valentino's death in 1926 caused mass hysteria among his female fans.  In Hollywood, many film stars were seen as sex symbols, such as  Errol Flynn, Gary Cooper, and Clark Gable. The "bad boy" image of the 1950s was epitomized by sex symbols such as James Dean and Marlon Brando. 
Elvis Presley obituary, Lester Bangs credited him as "the man who brought overt blatant vulgar sexual frenzy to the popular arts in America," in the 1950s and 1960s, through his overtly suggestive dance moves.
Fictional sex symbols
With regard to fiction,
Rotten Tomatoes states that the 1930s cartoon character Betty Boop is "the first and most famous sex symbol on animated screen".  Jessica Rabbit (voiced by Kathleen Turner) from the 1988 live-action/animation crossover film has been described as a sex symbol as well. Who Framed Roger Rabbit .  Toot Braunstein (voiced by Tara Strong) from the adult animated sitcom Drawn Together is also considered as a sex symbol. 
Video games have had a few characters that are considered sex symbols; one example would be
Lara Croft,   who has had several appearances in mainstream media. Other notable sex symbols include  Rayne, the first video game character that appeared in , in its October 2004 US issue's article, "Gaming Grows Up"; Playboy and  Nina Williams, voted "Hottest" Female Fighting Character in Guinness World Records, Gamers Edition 2008. 
"BBC World Service - Witness, The Death of Marilyn Monroe". BBC . Retrieved 2014.
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Pam Cook, "The trouble with sex: Diana Dors and the Blonde bombshell phenomenon", In: Bruce Babinigton (ed.), British Stars and Stardom: From Alma Taylor to Sean Connery, pp. 169-171. Quote: "- the sex symbol is usually defined in terms of her excessive sexuality"
Flexner, Stuart Berg; Soukhanov, Anne H. (1997). Speaking freely: a guided tour of American English from Plymouth Rock to Silicon Valley. Oxford University Press. p. 373. ISBN 0-19-510692-X.
Hutchinson, Pamela (22 February 2016). "Last of the red-hot myths: what gossip over Rudolph Valentino's sex life says about the silents". The Guardian . Retrieved 2017.
"The Queen at 90: The key events of 1926, in pictures". The DailyTelegraph. 21 April 2016 . Retrieved 2017.
Weinberg, Thomas S.; Newmahr, Staci, eds. (2014). Selves, Symbols, and Sexualities: An Interactionist Anthology: An Interactionist Anthology. Los Angeles: Sage Publications. ISBN 1483323897.
"Betty Boop: Boop Oop a Doop". Rottentomatoes.com . Retrieved 2014.
"Amanda Knox Is Like Jessica Rabbit". Sky News. September 27, 2011.
Barboza, David (19 January 1998). "Video World Is Smitten by a Gun-Toting, Tomb-Raiding Sex Symbol". . The New York Times
"Channel 4 Top 100 Sex Symbols internet poll". Channel4.com . Retrieved .
"Boom Raider". Telegraph. London . Retrieved 2008.
"AT's Top 10 Video Game Chicks". Actiontrip. Archived from the original on August 22, 2016 . Retrieved 2007.
Guinness World Records, Gamers Edition 2008 . 2008. p. 81. ISBN 978-1-904994-20-6.
Further reading Donna Leigh-Kile, Sex Symbols, Random House Inc, Aug 28, 1999, ISBN 188331951X