Who first claimed that "Gautama Buddha gained enlightenment"?

Some people said to me that , Gautama Buddha ***never made claims*** about himself that he had gained ***enlightenment*** and on the other hand, some people say that's not true. Some people have also said to me that this ***news of enlightenment*** was probably initiated by one of his disciples after his death. Here is ***my question***: Who claimed that ***Lord Buddha said that that "he obtained enlightenment"***?