Catherine II marries Ernest Frederick III, Duke of Saxe-Hildburghausen.
Were you not listening to telynk, TheBrunswickian, BBadolato or JonasResende?
Anyway, marriage didn't really work like that in those days - the husband was essentially the master of the wife in the eyes of most people, especially in Russia. It would take a very peculiar type of royal dude to marry a woman who ranked far higher than him. I'm not saying that wouldn't happen, or that it didn't happen occasionally in history, just that you can't just take any German Duke at random and say "Yes, this dude would be willing to be the junior partner in a marriage with a woman who was rumoured to have murdered her first husband, had numerous affairs with men and horses AND would be attractive enough personally and politically to Ekaterina herself that she would be willing to accept his proposal".
True, Hildburghausen was in major debt, but the family was quite chummy with Austria, supplying a few Field Marshals, etc. Why would that change? Anyway, Ernst Friedrich was married to his third wife from 1758 (when Ekaterina was still married to her first husband) to his death in 1780. Even if he outlived his third wife, why (other than love or greed) would he marry a menopausal woman with
her sexual lifestyle?