1. He never lost a military battle.
2. His battle strategies are still considered so efficient and effective that they are studied at U.S. military academies.
3. He rose from nothing to the highest position in the world (at the time); not an easy task in a society that is largely based on ancestry and wealth.
4. He left such a positive legacy with the Romans that his successors took his name, and even the leaders of Russia were named after him (czar).
There are a number of areas in which Caesar is considered to have amassed a variety of impressive accomplishments, for many the first would be the military campaigns he directed to great success. One of the most widely known and most successful was his campaign in Gaul where he extended the borders of the Roman Empire while also further enriching himself and helping to give him more power when he would return to politics.
He also gained an enormous amount of power coming from a relatively humble background, and eventually shared power in the first "triumvirate" to share power as he had difficulty winning the power outright. He managed to become so popular that he was later assassinated by a group which thought he had grown too powerful for his own good and would have made himself emporer.