Maha makes a brief cameo appearance during Killua's deduction of everyone's relationship with each other in the family. Maha basically has no relationship of any kind with anyone in his family and vice versa.
Maha is the only known Enhancer in the Zoldyck Family. According to Zeno, Maha was incredibly powerful in his youth, to the point that Isaac Netero, once considered the strongest fighter in the world, received praise just for surviving a fight against him: he was, in fact, the only person that far to challenge Maha and live to tell the tale. However, the statement could also be taken to mean simply that Maha and Isaac have fought in the past and, prior to the latter's death, were both extremely long-lived. It is unknown if Maha's strength has waned with old age.
In the official databook, his name is also spelled as "Mahha Zaoldyeck".
His name is not given in the manga nor in any of the anime adaptations, having been revealed in the official databook.
In Coco Loo's explanation and according to the 2004 databook, Maha is Zeno's father. However, in Chapter 264, it seems as though Yoshihiro Togashi retconned him as being Zeno's grandfather. His age may have been changed as well, since the family tree lists him as being the same age as Isaac Netero.
It is also possible that Maha and Zigg Zoldyck are the same person and that his name was retconned along with his age and his relations to the rest of the family.