Since his transformation into a chimera, it's most likely that Zelgadiss had few people he could call "friend." Zolf and Rodimus were probably the first people he could trust and rely on more than anyone else after Rezo's treachery, and he would soon come to regard Lina, Gourry and Ameria as irreplaceable companions. Although he may come off as being coldly neutral, he really does care about his companions and would go to any length to help them out. He may complain about their bad habits and lack of focus when it comes to completing goals, but to Zelgadiss, there is nothing else that he believes to be more valuable than his friends. After all, his friends are the people who look past his condition and see him for the person that he truly is.

Zolf & Rodimus
It's never said how Zolf and Rodimus came to be Zelgadiss' companions, though it's probably safe to say that they met each other under Rezo's employ. I believe that Zolf and Rodimus, being good-natured people themselves, saw what had happened to Zelgadiss and found the good in him. As they worked together, the closer they became. Both are fiercely loyal to Zelgadiss and never hesitated to follow him after he turned away from Rezo.

Zelgadiss also highly regarded Zolf and Rodimus. When he found out that, unlike Dilgear, the two men decided to continue to show their loyalty to himself, I think he was relieved that he really could call them friends. When they died after Ruby Eye Shabranigdu's resurrection, Zelgadiss was grief-struck but dealt with the comfort of believing that the two would undoubtedly be waiting for him in the afterlife.

Lina Inverse
Right from the start, Lina quickly pegged Zelgadiss' personality as a man who keeps his word. While the two didn't exactly get off to a good start, they did manage to get along very well in a short amount of time after Zelgadiss decided to help her escape from Rezo's stronghold. Lina quickly learned how much of an asset Zelgadiss could be and began to see for herself that he really wasn't a bad person at all; just very troubled due to the things that have happened to him in the past. Lina was probably someone that Zelgadiss needed in his life at the time; someone who had more of a light-hearted view of the world and who could show him that not everyone would judge him based on his appearances.

Over time, both Lina and Zelgadiss came to the point where they could trust each other as an intelligent source amongst all the chaos they encountered. Lina most likely feels relieved to have Zelgadiss around in times where they learn some serious information, as he's usually the only other one to seem to know what's going on and come to the same conclusions with the situation at hand. Their personalities do clash of course, since Zelgadiss is extremely goal-oriented and tends to severely dislike Lina's habit of going on detours. Still, despite any grumbling he may do, he really is greatful to have Lina as a friend and would go the distance to help her out when she needs it most.

Gourry Gabriev
Considering that Gourry could never seem to care enough to remember Zelgadiss' name, it can be said that the two didn't really get off to a good start either. To Gourry, Zelgadiss was an enemy and a threat to Lina and similarly, Gourry was nothing more than an obstacle in Zelgadiss' path. However, there was never anything personal between the two and they both seemed to accept each other and get along just fine once they joined forces.

They're also probably glad to have each other around when situations start to get out of hand; Lina and Ameria can be a handful at times and I think both guys feel relieved that when the girls start to get worked up about something, they can share a calm moment of sanity with each other. They've also teased each other about the situation they've gotten themselves into, and end up being the only ones who really feel really sympathetic for the other after he becomes the focus of some extreme scheme for something.

Ameria Wil Tesla Saillune
While the anime has Zelgadiss and Ameria starting off to a rather rocky start (no pun intended) with Ameria immediately assuming Zelgadiss is someone not to be trusted based on his looks, the novels are quite different. Ameria never jumps to conclusions about Zelgadiss; in fact, she doesn't even hesitate to jump into battle and help him out! I think in all versions, the two don't start off as the best of friends but as time passes, they slowly begin to spend more time with each other (especially in the cases where Lina and Gourry are off on their own).

I think it's pretty safe to say that Zelgadiss and Ameria have a relationship that goes beyond simple friendship. Please see this section for more information.

Sylphiel Nels Lahda
The majority of the interaction between Sylphiel and Zelgadiss takes place in the anime, as they barely interact in the novels at all. When they first meet, Zelgadiss is rather harsh with Sylphiel; when she witnesses the destruction of her town and is mourning the loss of her father, Zelgadiss scolds her about it and tells her bluntly that if she continues to just sit and cry that more people will die just as her father did. To the rest of the group, this comes off as being incredibly heartless but Zelgadiss was really just trying to help her come back to reality. He really did have her best interests in mind, it just didn't come out in the nicest way.

Before Xelloss' initial appearance in the novels, he had already encountered Zelgadiss and had managed to give the chimera a pretty terrible first impression -- not only did he kill a creature that Zel had felt somewhat sympathetic towards, he also resurrected a girl right in front of Zelgadiss' eyes. So needless to say, even though they had temporarily allied with each other in order to find a copy of the Clare Bible manuscript, Zelgadiss didn't trust Xelloss one bit. This complete dislike for Xelloss was cemented when the mazoku burned said Clare Bible manuscript right in front of Zelgadiss' eyes. Destroying the only piece of hope Zelgadiss had at the moment wasn't exactly the best way to make friends (which Xelloss never intended to, but all the same).

In the anime, Zelgadiss becomes a ticking timebomb whenever Xelloss is around; he has little patience for the mazoku and is usually the one that's unable to tolerate his antics at all. In the novels, while he doesn't have a lot of patience for Xelloss' shifty behaviour, he still remains surprisingly civil around Xelloss and manages to keep his cool. In all versions of the series, as time passes, Zelgadiss begins to pay attention to the more important matters at hand and gets less bothered by Xelloss, perhaps getting used to his annoying personality. Still, all said and done, Xelloss is definitely Zel's least-liked person.