This from The Scotsman.com:

Groundskeeper Willie is the classic Scot for Americans

A HOT-headed school janitor from The Simpsons inspired by a herbalist from Leith has been named the Scot most Americans associated with the country. A survey found that grumpy Groundskeeper Willie from the TV cartoon is the character they most believe personifies the Scottish temperament. The finding emerged in a report commissioned to gauge the impact of efforts to promote Scotland in the US.

It found that Americans see Scotland as “backward and oldfashioned”, with most of those surveyed unable to name a single Scottish city.

Simpsons creator Matt Groening has admitted he got the idea for Groundskeeper Willie from an “angry Scot” character who appeared in a 1980s sitcom and was played by comedian Dave Thomas.
The character was inspired by the actor’s real-life grandfather, William C. Muir, from Leith.

http://news.scotsman.com/scotland.cfm?id=1501312007