I remember being an eleven-year-old kid playing what will always be Final Fantasy 2 in my heart (though not my mind) for the first time. I had just struggled past these 3 wicked ass sisters that seemed able to destroy my hopes and dreams over and over before I pressed on to meet this character that was the master of the seemingly chaotic element of fire. I had already seen him mop the floor with Edge, and I was intimidated. Then I met him. He greeted me with a revelry that has not been matched since. My friend and I talked endlessly about the first boss that seemed to match the knight that wanted to knock us all down in coolness of sprite look. Rubicant was that villian that was so self confident and kind that he was willing to heal us to give us a better shot at beating him. How he had gotten mixed up with Golbez perplexed me then as now, but later in life, I came to recognize him as the most lunarian of the fiends, emperors, whatever. His sense of justice was unparalelled and seemed to dwarf the sense of righteousness of my own party, and this led me to ideas that are relevant even today. This curiousness about what makes right, right or vice versa. Later in the game, my party was proven the pursuers of peace, and that alone justifies actions that many would consider barbaric, but what if we'd been wrong? Rubicant would then have been the most virtuous being in the game, and it must have been toward these sensibilities that Golbez was able to flatter Rubicant into his party.

Short answer: Rubicant is the most awesome fiend ever and the only one to come close is Tiamat.

p.s. One can only wonder what Rubicant's shorter party-sized self would have looked like, but I bet it would have been frikkin' awesome.