In one sense elliptic curves are a rather modern object as some of its properties have been studied only in the last century or so. But in another sense there are a very classical object for studying Diophantine equations. For instance it is possible to be "using" them implicitly and proving facts about them without actually knowing the formal concept like Ramanujan did with modular forms.
So my question is what is the history behind elliptic curves? When was the notion formalized and by whom? Any references to this?
I just finished taking a graduate course in Elliptic curves from Ezra Brown here at Virginia Tech. He loves to write expository articles in mathematics and I just realized (not surprisingly) that he's a co-author in the article cited by Alvaro. You might want to take a look at some of his other articles, here's another one:
Brown, Ezra, and Bruce T. Myers. “Elliptic Curves from Mordell to Diophantus and Back.” The American Mathematical Monthly, vol. 109, no. 7, 2002, pp. 639–649. JSTOR, www.jstor.org/stable/3072428. Accessed 20 Apr. 2021.