The movie "The Patriot" was based on many actual events. Some of the characters in the movie were based on actual people but just had a different name. Many battles in the film were actual battles. The historical events in the film were very accurate, but they were not named. .
The character of Benjamin Martin was originally meant to be The Swamp Fox, Francis Marion, but for the sake of telling the best 'dramatic' story they could, the filmmakers fictionalized the character and the story. They then added elements of the historic figures of Elijah Clarke, Brigadier General Daniel Morgan, Andrew Pickens and Thomas Sumter to the character of Benjamin Martin. Such a move also depicted historical inaccuracies that always appear in movies. .
Martin's hit and run tactics and famed nickname were inspired by Francis Marion, while the tactics of using the militia on the front to draw the British in the final battle were based on similar tactics used by Daniel Morgan at the Battle of Cowpens. Thomas Sumter and Andrew Picken's influence seems to be that both rejoined the fight after the British burned their homes and in Sumter's case, made his wife and son watch the house burn.
General Charles Cornwallis was an actual historic figure and not merely a character suggested by a historic figure. The personal journals that Martin captures in the movie were also real and Cornwallis later published them in several volumes. Cornwallis was born into new British nobility and spent all his younger years in noble circles. He purchased a commission in the British Army and then actually studied for it. He proved to be a successful and competent officer.
As far as the movie goes, Cornwallis was not as old as he is portrayed in the movie. In reality, he was in his early 40's during the war. All indications were that he wasn't as pompous as sometimes depicted in the movie. As a matter of fact, he was known to be popular with his men, because he went down to the battlefield and into danger to encourage his men, rather than simply remaining at a command post far away from danger as depicted in the movie.