In the times of Ancient Egypt they were the advisers of the pharaoh. The Chief Lector's role is to serve and protect the Pharaoh who take care of the crook and flail, and they take their place at the foot of the throne. Also, Iskandar appears to have some special feelings for Zia because it turns out Iskandar has to protect her because she is hosting Nephthys. When the former Chief Lector dies, he or she is then replaced by the second most powerful magician. Meaning, Iskandar was the most powerful magician, followed by Desjardins and Amos Kane. When Desjardins became the Chief Lector, Amos Kane was then the second most powerful and Vladimir Menshikov the third most powerful magician. When Desjardins died, Amos became the first most powerful magician and the new Chief Lector. Although Carter Kane is now Pharaoh, he has left the day to day running of the House of Life in the hands of Amos while he runs Brooklyn House. That's a little weird actually. Wow.
Chief Lectors possess the power to summon Sekhmet once during their lifetime. Desjardins used it soon after he became the Chief Lector, as he was never patient. Amos has not used it yet, and it is unknown if Iskandar used it.