Its a very indepth topic, but I chose field marshal because I feel it best captures the full intent of how the title was used.

Originally imperator was more of a mere description referring to anyone who holds imperium, but over time it started to be used as a specific title that would be acclaimed by high ranking men after great victories. And then under empire was highly restricted to essentially only the main leaders. Added note in roman society 'command' was a significant status with significant legal implications and not something to be viewed as just a "military leadership" role

The closest parable to this sense is the 5 star marshal rank, which is a supreme rank but is not a standard position but instead typically given as an honor after wars and victories to leaders of militaries. And in fact dictators often take field marshal as their key title for much of this reason.