I’m going to answer this question historically as opposed to using gnosis.
So, originally, satan was not a name it was a title, הַשָּׂטָ֛ן “hashaytan” which means the accuser. It was an angelic entity whose job was to accuse men before God (Job 1:6-12; 2:1-6; Zechariah 3:1-7). In the Septuagint this word was translated as diaboloß “diabolos” which means the slanderer, literally to throw across from διά “through, across” and βάλλειν “to throw”. Diabolos is where we get the word devil from.
Anyway, so during the Babylonian exile, the Jews interact with the Persian Zoroastrian religion. I go at length into this process in this post:
And after this event, we see the only instance of Satan being used as a name in 1 Chronicles 21:14.
tl;dr Satan is a mask of Ahriman.