Gabriela Sullivan is Zack's adoptive mother. Gabriela was single with no children of her own when someone left Zack on her door step when he was only a baby. She was overjoyed and became almost instantly attached to Zack, as she did not have any kids of her own at the time; she began to raise Lewis as if he was her own. As Zack grew, his attachment to Gabriela only increased but when it was revealed that Zack was actually part demon and possessed super powers, he thought that she would look at him in a different light. This made Zack both nervous and scarred; he feared that she would shun and ostracize him but she instead embraced him, exclaiming that everyone has “special gifts” and this was simply one of them. After his lineage was revealed, she was the only person that still viewed him as Zack Sullivan, not the demon who can tame lightning and he loved her dearly for this. When Zack found her dead, he was heartbroken; he had lost a women that was closer to him than anyone had ever been before.
Seth Richards is the leader of the The Acolytes and is therefore Zack's leader and boss. Zack views Seth as a strong ally and a reliable leader but Zack does not have that many other viewpoints on Seth; if he gets Zack's back, then Zack will get his. He also wants to help Seth fulfill his prophecy and really wants to help fight Kan'il-El, an opponent who he believes will be a worthy adversary.
Loran Constantine is the granddaughter of John Constantine and also possesses DNA that is partially demonic in nature. Because of this, Zack found himself instantly attracted to her, something that he had never experienced before in his life. He feels that she has a strong understanding of him and what he experienced as a child because she most likely had similar occurrences, as well. He hid his true feelings from her for quite a while until Papa Midnite gave him the courage to tell her how he really felled. When Zack confessed his love for her, he found out that she had feelings for him to and that she was as nervous as he was. This relieved him to a great extent and even led the two to begin courting each other as boyfriend and girlfriend.
Zack first met Griger in the back streets of New York City. He was investigating Sportsmaster when Zack accidentally stumbled upon the deal he was making with local mafia. When Griger realized the deal was broken up by Zack, he was initially mad at him, but when Zack agreed to help him solve the problem. After the problem was solved, the two appeared to have made a connection and a friendship that can be counted on at a later date.