Zaros (also known as The Empty Lord, Great Lord and God of Unknown Power) is a god whose arrival in Gielinor was one of the most important events of the early Second Age. During this age, he ruled a vast empire stretching from Ice Mountain in eastern Asgarnia to Canifis in Morytania, and from Ghorrock in the north of the Wilderness as far south as Ullek as he waged war against the Kharidian Desert. From his arrival soon after Guthix entered his first great slumber until his downfall at the hand of Zamorak, he was the most powerful god known on Gielinor both in personal power and influence. Zaros is the patron of the Ancient Magicks and Ancient Curses, and is associated with conquest and domination. Zaros has recently regained contact with his followers on Gielinor by way of the Communion Portal.

Present-day Saradominists and Zamorakians consider Zaros an adversary. Others, like certain inhabitants of Kharidian Desert and some Mahjarrat, still worship Zaros as their lord. There is currently no indication as to Zaros's motives, other than that the player may be part of his plans at some point in the future.

Saradominists such as Lennissa have claimed that

Evil will always breed more evil, and will never be satisfied with what it has. The Empty Lord chose to ally himself with the dark creatures of this world, fully aware that their own natures would cause them to rally against his rule, and take every opportunity they could to betray him.

— Lennissa[src]

Some of Zaros' followers are evil in the conventional sense of being ruthless, enjoying being deceptive and seeking power for power's sake. In addition, the Ancient Curses seem to be evil (or at least highly combative) in nature: they focus on inflicting damage on others and draining others of their powers. Although some may jump to the conclusion that Zaros is evil, evidence is inconclusive. It is very likely Zaros' army of demons and vampyres committed evil acts, but there are no records of Zaros himself promoting evil: however, it is likewise true that there are no records of him promoting good. Additionally, even creatures who did not and do not follow Saradomin or Zamorak, such as the Pharaoh Queen, call Zaros a 'vile creature' whom they clashed against long ago, though this may be due to his war with the Menaphite Pantheon.

Zaros's legacy is still strong, as Saradomin will not speak of him, instead making evasive responses; when asked about Zaros by a player in the God Letters, he refused to say anything: "For your own continued good health, I implore you to drop this subject. Speak that name no more, and trouble not your mind with such thoughts."

Zamorak fears him immensely, as a reborn Zaros would be sure to seek out vengeance against his betrayer.

According to the Mysterious ghost, "As I told you, the Empty Lord was extremely powerful, but not so powerful that he could rule over the other deities of this world. Should he have made a move against any other god, then he could still have been easily brought down by the combined efforts of the others." With the aid of the Staff of Armadyl, though, Zaros's power would have been magnified to a degree enabling him to overcome all the other gods; however, due to interference by certain followers of Zamorak and Saradomin, he failed to obtain the artefact.

Notable followers of Zaros include the Mahjarrat Akthanakos, Azzanadra, Jhallan, Sliske and Wahisietel. Traditionally, the vampyres, dragon riders, and demons of Gielinor were allied with Zaros, but most, if not all of these, switched their allegiance to Zamorak once he defeated Zaros.