From the Literal Translation Project:

Humans found a god, and thus, tried to obtain it. As a result, humanity was punished. That was 15 years ago. The god that they found vanished. However, they tried to revive the god themselves. It was Adam.

This heavily implies that Adam and the Giant of Light are actually two distinct entities, with the former being created from the latter. However, Gendo told Fuyutsuki back in 2003 that Adam and the Giant of Light were the same thing.

So... what gives?

EDIT:

Ritsuko also claims that the Evas are artificial humans made from Adam. However, humans are Lilith-based lifeforms, not Adam-based ones, so wouldn't that mean the Evas are artificial Angels, not artificial humans?

Well the first thing to note is that “Adam” is just an arbitrary name that some people gave to something. When Ritsuko refers to “Adam” she seems to be referring specifically to the Adam embryo that Gendo gets his hands on (literally, lol), whereas Gendo seems to use it to more generally refer to the giant of light, who after the events of Second Impact somehow ended up in a dormant embryonic state - either because Gendo’s crew did something to incapacitate it, or because it died and all Gendo’s crew could save was the little embryo. Whether the giant of light and the Adam embryo are the “same being” are up to one’s subjective interpretation, and evidentially Ritsuko and Gendo disagree on this matter.