Hi everyone, Granted, it was on Wikipedia but I remember reading about the rise of early christianity in the Roman Empire and about the polemics aimed at the figure of Jesus and christianity as a whole. There was a Greek philosopher who basically argued that "there already was a famous Greek man who performed miracles and other feats and we have proof of his existence, why not worship him if there is absolutely no proof of Jesus?". Not a direct quote by any means but that was the crux of it. Who was the author of that claim? Who was he referencing? Who were the biggest outspoken critics of the early christianity? Where can I read more? I am aware of the broad scope of the question so please forgive me but it sits on my mind for two months already and the unfruitful search for answers only ignited my interest further.
You are more than likely thinking of Celsus who wrote his On True Doctrine (Λόγος Ἀληθής) in the late 170s, possibly in response to the work of Justin Martyr. We only have this work in fragmentary form thanks to Origen's (d. 253) Contra Celsum (Against Celsus). Celsus therein argues that Jesus is not only similar, but inferior to other gods. Asclepius had returned from the dead and done so for longer and more clearly. Celsus likewise mentions people like Aristeas, who could vanish and reappear (Contra Celsus 3.3). Nobody counts Aristeas as a god, so why would anyone think of Jesus as one?
If you want to read more, check out Origen's Contra Celsum. You may likewise be interested in the work of Justin Martyr, who lived contemporaneously with Celsus. Augustine's On the City of God is also a very good work for seeing how later Christians responded to pagan critics. For other pagan critics of Christianity in antiquity, check out Porphyry's (d. 305) Against the Christians as well as Julian the Apostate's (d. 363) Against the Galileans.
For academic works, check out Robert Louis Wilken's The Christians as the Romans Saw Them as well as Jeff Hargis' Against the Christians: The Rise of Early Anti-Christian Polemic.
You're probably thinking of Apollonius of Tyana, who has been frequently compared with Jesus in anti-Christian polemic ever since an imperial official named Hierocles did so in his book Lover of Truth. The Life of Apollonius of Tyana by Philostratus is available in an edition and translation by Christopher P. Jones in two volumes from the Loeb Classical Library, with a third volume containing the surviving letters of Apollonius, things said about Apollonius in the writings of other ancient authors, and a rebuttal to Sossianus Hierocles by Eusebius of Caesarea which calls into question both the reliability of Philostratus' astounding tales and the moral character of Apollonius according to what Philostratus reports.