Eternity is endless and unending time. It is a state to which time has no application. Something which is eternal is not moving, and is beyond time.[1] That is to say, it has always existed.
As for the reality of the Commander of the Faithful, Ali (a.s.), if you mean his material existence, it is clear that his material existence is not eternal but if you mean by the word “reality” the Imam’s existence and creation out of light or in other words his existence as a result of the existence of cause, we can say that his existence is eternal. Obviously, the existence of any entity other than God is shadowy and subordinate to God’s existence. So are the attributes of a shadowy existent.  Based on a monotheistic worldview, only God’s existence and His attributes are real whereas other existents are in need of God and dependent on Him. If there is any eternal being other than God, it would definitely be in need of God and dependent on Him. It would need God from eternity.
The Fourteen Pure Lights i.e. the Holy Prophet (pbuh) and his Ahlul-Bayt (a.s.) are the complete and perfect expression of divine attributes.  He who knows them knows God in the best manner. Although the infallibles (a.s.) are creatures, they can be subordinately eternal in terms of their creation out of light and materialization of cause. Therefore, the traditions which indicate that they were the first light and creatures are not in contrast with their eternity in terms of the existence of their light.  For example, Jabir bin Abdullah narrates from Imam Baqir (a.s.) that he said: “Muhammad (pbuh) and the Infallibles are the first creatures.”[2]
Also Imam Reza (a.s.) has been narrated as having said: “The first thing that God, the Exalted created were our souls.”[3]
For further information in this regard, refer to question 2229 (site: 2525) Index: What is the relationship between the attributes of action and the temporal events? ), and question 2217 (site: 2359) index: Proving God’s Eternity.

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