The character George in Blackadder III was clownishly stupid, and recognized himself to be so. He knew his mental limitations, but was willing to give anything a try, perpetually failing at the task.

George IV was not the same. He was recorded as being a smart student, but tended to fail at the big picture issues and was a public relations nightmare. He received an enormous allowance but managed to spend even more. He had a secret marriage that was not recognized by the establishment, is rumored to have had several mistresses, then put his legal wife on public trial for adultery.

"Gormless" is not a word that I hear very often in American lingo. To which George would it apply?

I haven't seen Blackadder III, so I can't tell you if he was depicted correctly, but I can assure you that the Prince Regent (later George IV) was anything but "gormless". (Great word, by the way... had to look that one up!) George was many things, but not even his harshest critics could accuse him of being unintelligent. It wasn't that he didn't understand politics; he was just more interested in other things (namely women) and was easily swayed by the people he liked/trusted. While he may have had his vices, he was the result of his upbringing, having been both ignored and spoiled absolutely rotten by his parents.

He was naturally gifted, was well taught in the classics, learned to speak French, Italian and German fluently, and had considerable taste for music and the arts... His tutor, Bishop Richard Hurd, said of him when fifteen years old that he would be "either the most polished gentleman or the most accomplished blackguard in Europe -- possibly both"; and the latter prediction was only too fully justified. http://www.nndb.com/people/395/000093116/

As a young man, George became a leading figure in fashionable society and was known as the first gentleman of Europe for his polished and refined manners. He was to become a lavish, even extravagant patron of the arts and possessed both charm and taste. George was an avid reader of the novels of Sir Walter Scott and Jane Austen. He established a superb collection of paintings and had a keen interest in architecture. http://www.englishmonarchs.co.uk/hanover_4.htm

George IV's undoubted charm, his evident wit, his innate aesthetic sense, his enthusiasm and his imagination still left him ill-equipped to rise to the challenge of a nation daily growing in self confidence and wealth. His self-indulgence and short attention span, together with his evident ability to abandon political principles and to forget friendships with barely a backward glance, won him little praise. http://www.bbc.co.uk/history/british/empire_seapower/george_fourth_01.shtml