Genghis Khan. I kind of abhor killing people for stupid reasons, like race or religion. However, this does not mean that killing is something I actually despise. I think that given the brutality of those times, the Mongols were simply the best at what they did.
I guess I respect him for being absolutely merciless to his foes and generally better than most rulers to those beneath him. He promoted generals regardless of birth, nationality or religion. In fact the Mongols allowed complete religious freedom. If people surrendered they were spared, if not they ceased to be (unless they did well in battle at which point they'd get a second offer to join the Horde). Dishonest tax collectors were executed and put on public display. Arrogant enemy rulers were brutally murdered, in one case by having molten metal poured in his eyes and mouth. Whole regions of the world turned from green pastures into dead deserts because the Mongols salted the land and diverted rivers if it had to be done. They spared scholars and learned men. He lead his people out of the Steppe and into China, into the Middle East, into Europe, and into India, each spawning seperate Mongol empires. Some of these empires went on to be powers for centuries like the Mughals. Other times the nomads resurged in their bloodthirsty ways, like Temur the Lame.
Genghis himself survived the murder of his family, living in exile with his mother, took over a tribe for himself, united the Mongols and other nomads, and went on to grab the world by its throat and hang it out of a window while it's emperors, kings, and holy men cried to a sky that held no answers.
He wasn't a good guy, but he earned every coin, every piece of ass, and every tract of land against overwhelming odds.
My second would be Castro. A dictator? Yes. A killer? Sure. He is though one of the few that strove to at least provide for his land and guarantee independence. The US was not an honorable or well intentioned opponent, and Castro fought us as such. I think the time he emptied the Cuban prisons and exiled them all to the US is actually pretty god damn funny. He could have made a complete hell hole, and although Cuba isn't great, they do have good health care and education. I admire him for standing up to American business interests and their fascist bullshit.