Professor Smith maintains that the Loch Ness monster exists. Everyone knows Smith is a communist. This fallacy occurs when someone attempts to refute an argumentative claim by attacking a person's character. The argument is logically invalid because the premises are irrelevant to the conclusion. A person's character or social standing has no logical relation to the truth or falsity of a given claim.
Extraterrestrial intelligence exists in the universe.
You can have no doubt about this because Robert Stack said so and he is the host of the television show Unsolved Mysteries. Extraterrestrial intelligence exists in the universe. You can have no doubt about this because Professor Williams said so and he is a tenured professor in the Civil Engineering department. Extraterrestrial intelligence exists in the universe. You can have no doubt about this because Frank Drake, a leading astronomer, has formulated an equation that estimates 10,000 to 100,000 advanced civilizations exist in the Milky Way galaxy alone.