GREAT QUESTION!!
My easy answer is, of course, my baby boy Julian The Apostate, who, after the christianization of Rome, had a really wacky idea to go back to the pagan stuff, and was tragically killed in a stupid battle in a stupid way before he was able to do anything about it.
Like yeah it's a bit goofy to assume he would have been able to singlehandedly turn back the clock on Roman Christianity, but it's one of the great what-ifs of the time. Even if he couldn't, he could have done something different and that's fascinating to think about.
OOOOO or Elagabalus, who as I've already goofed about in that link was a PROUD bottom in a way that made conservative Romans very uncomfortable, BUT ALSO tried to make pre-Christian Romans into a monotheistic society who worshipped only a sun god called "Sol Invictus".
But honestly that's just the tip of the iceberg with Elagabalus. He also married a Vestal Virgin, a holy woman of Roman religion, which was of course SUPER uncouth. It's possible some of the notes about his sexuality were embellished by later writers hoping to throw dirt on his name, but a lot seems hard to dispute. It's possible that he considered himself some form of non-male, rumors abounded that he referred to himself as a "queen" or the consort of his gladiator boyfriend. There's just so much with him.
OR maybe Diocletian, an emperor so famed for his expertise and bureaucratic skills that he got to RETIRE (as in, not be killed by a usurper, a very rare honor) and went to his family home to farm cabbages.
His form of government, the Tetrarchy, turned out to only last about a generation, before later years left greedy sub-emperors once again fighting over the Empire. The people of Dalmatia supposedly begged Diocletian to return to service, but in an incredible line, Diocletian was said to have replied,
If you could show the cabbage that I planted with my own hands to your emperor, he definitely wouldn't dare suggest that I replace the peace and happiness of this place with the storms of a never-satisfied greed.
Once in a generation statesman, but apparently an amazing cabbage farmer.
