It is a fair question to ask (your title question), especially since neither he, nor his angels are accounted for in the Creation story of Gen 1&2. But let me first say this; you should 'Let God be true, but every man a liar'(Rom3:4) if you want to learn the Truth. To this end (convince yourself), if u accept Gen 1&2 as the complete and perfect account of all HE created and made during Creation, then
Adam, who was the only being created in the Image and Likeness of the LORD (EZ21:26-28), and who was given dominion over the Garden and the earth, and who was given a promise of eternal life for obedience to the Commandment (Don't Eat (sin)), and who was the only person to whom the Lord spoke the Truth, must be that Annointed Cherub that Covereth, whom is Lucifer, who became the serpent, devil and Satan (others names also), who too was created perfect and shown of beautiful colors, and who too was given dominion, and who too knew and was to abide by the Truth (Jn8:44). But, if you let men add to this account, then there are wide variety of interpretations you will have to sift through. But let me ask you some questions that might help you to understand it all.
How is there a serpent already in the Garden, even before Eve sins? Has not one already earned the reputations of being subtle and being as a serpent? The HEB
word for serpent, and the root is comes from imply the serpent is one who speaks a lie or enchantment. So has not the serpent already lied? Is Eve's testimony of the Truth the absolute Truth as was told to Adam, or how is that she spoke untruth unless it was something told to her which she believed (this would have been the first lie told)? How is God just in condening the serpent without a trial, unless the serpent is Adam, who already gave his testimony? Is not the serpent's curse the curse of sin all are born under since Adam sinned: for it is not found in the curse upon Adam ( acurse upon the flesh)? Did not Jesus's mother have to be a virgin, in order to fulfill that condition of the serpent's curse which excluded his seed from having any part in the Savior?
Read Ez28, Is14 and consider this with Adam.