Well, there was Mithra... some say we ripped off Christ from that.
1. there’s precious little actual evidence as to what the cult of mithras beleived.
2. there’s zero proof as to which influenced which. (but a ton more actual evidence as to when christianity was founded, and what it beleived and when)
3. st paul traveled to antioch (i’m fairly sure it was antioch) where the cult of mithras was prevelent, this is used to suggest he copied parts of the mithran ideas; hint: it’s just as likely that the Christianity St Paul preached had an influence on the cult of mithras!
4. 90% of the similarities ascribed to the cult of mithras and Christianity are laughably untrue. For instance Mithras was aledged to be born of a virgin in a cave. this is true in as much as mithras was born out of a rock which presumably left a cave in its wake and presumably had never had sexual relations with any other rocks.
Or the other way around. The cult of Mithra became popular at the same time that Christianity was growing. In many ways, the baptism rite of the cult of Mithra probably came as an idea from Christianity. It certainly didn't predate it.