Perhaps one day we will make MaleOrNotMale.com (but don't bet on it). If we ever do, Kodos will be one of the first profiles. You see, in one of the episodes, Kang refers to Kodos as his sister. In other episodes, Kodos is referred to as male.
Maybe the concepts of religion and gender are a bit different on Rigel VII than on Earth?
Who are we to say?