I can think of a few dozen empires in history that were hereditary, but I can't think of one that wasn't besides the Holy Roman Empire, and even they were essentially hereditary for the most part.
Egypt had a interesting ruler system. If I recall correctly, it was passed between family members, but not from parent to child. It passes from the current ruler, to next oldest sibling of that ruler, and then it passes down to the oldest sibling's oldest child, and goes through his siblings, then it passes back up to the next oldest sibling's oldest child, and so on. Basically the oldest living relative, with older generations getting priority even over older individuals of a younger generation (find oldest generation -> find oldest relative in that generation).
Note that 'sibling' can be male or female. They'd also intermarry to strengthen and consolidate power, and so there would be co-regencies of two people ruling at once with more or less equal authority, or with one (either female or male) wielding more power than their spouse.
I might be mistaken about this though - I never studied the topic and only heard about it from others.
Aside from Dune which was more about planet ecology than interstellar politics there are almost no examples of imperial systems in speculative fiction. Sometimes you have them in role playing IPs but that's because its "cool" and "epic."
