Can't decide out of this lot:

Science:
- Charles Darwin
- Albert Einstein
- Watson & Crick
- Archimedes
- Imhotep (Egyptian medic and architect, much of Hipocrates' teachings were based on Imhotep's, but Imhotep did it over 1000 yrs before)

Civilisations:

- Ramses II
- Genghis Khan (supposedly 1 in 10 people can trace their ancestry directly to this guy... frisky bugger)
- Alexander the Great
- Julius Caesar

Not sure about greatest but influential:

Religion:
- Jesus Christ
- Emperor Constantine
- Mohammed
- Buddha

And just for laughs:

Finctional:
- Gordon Freeman
- JC Denton
- Solid Snake
- Mario
- Link
- Master Chief
- Shepard
- Neo
- Emperor Palpatine
- Darth Revan

Gaius Julius Caesar Augustus is the greatest man to have ever lived imo. He finished what his "father" started.
Jesus is nothing more then a made up story based on some real stuff.

4% in Europe can trace their ancestry back to Charlemagne the Great. If you're family lived somewhere near Belgium during his reign then you're most likely related to him.

Definitely my father!!

So did George W. Bush. That make him a great man?

Muhammads up there.

Not only was he a spiritual leader (and Islam will probably take over Christianity as the most popular religion eventually) but he was also a political and military leader aswell. Pretty much a jack of all trades fella.

Quote from wiki "He was also active as a diplomat, merchant, philosopher, orator, legislator, reformer, military general, and, according to Muslim belief, an agent of divine action."

Being agnostic I refute the last point, but he did a lot of stuff.

Not a big fan of religion but outside of the obvious (Jesus) and some of the great philosophers, writers and scientests he's pretty much the top.

You could also write a long list of Greeks from the classical period that'd be ver valid aswell.

That's mostly only because the Gregorian calender is practical. In fact most countries reject the religious meaning and do away with B.C. and A.D. and replace it with B.C.E. and C.E., effectively making the calender secular. They don't use it because of religion, they use it out of practicality.

That aside, other calenders are still used around the world, there's the Islamic calender, the traditional Chinese calender, the traditional Indian calender, the Buddhist calender.

Please don't compare morons to a genius.  Bush finished nothing by the way. 

Augustus brought an end to the worst form of leading a big empire/country. A republic. Bah...

Just something to think about when looking at political history from more then a few hundred years ago...

The winners write the history. Any leader in those days could have been a Stalin. If Stalin had gotten to write our history, in 1000 years people would look back on him as a great leader. In fact the greatest of our time.

So, I try and take all that really old political stuff with a grain of salt.

Actually, compared to all other Roman emperors he was a pretty decent guy. 

You also can't compare leaders of 2000 years ago with leaders of 50 years ago. By todays standards Augustus would be a very harsh ruler. Doesn't mean I can't think of him as a great guy. Most of the great guys in history are mass murderers like Caesar(not Augustus, the real one), Alexander the Great, etc

Caesar killed of 25% of population in Gaul, yet a lot of people still admire him today. There was not a single Roman who thought of Caesar as a mass murderer. They simply didn't care about the well being of the "barbaroi"

If you're going to compare leaders then you need to take time into account as it's really important.