The Ghost of George Washington
Excerpt from Wikipedia George Washington was an American political leader, military general, statesman, and Founding Father who served as the first president of the United States from 1789 to 1797. Previously, he led Patriot forces to victory in the nation's War for Independence. He presided at the Constitutional Convention of 1787, which established the U.S. Constitution and a federal government. Washington has been called the "Father of His Country" for his manifold leadership in the formative days of the new nation.
In the episode George Washington, Dan becomes convinced the ghost of George has cut down a palm tree near Casa Paradiso, crushing his car. While it's never made explicitly clear if this was true(The fact the ghost has a separate, spectral axe suggests it wasn't him) at the end of the episode we see the actual Ghost of George Washington. He is EXTREMELY furious to discover Dan has altered his diary to mock and demean him, and, grabbing a ghostly axe, vows revenge on Dan.