The Answer:

The invention of the monkey wrench has been attributed to a man named Charles Moncky, who is said to have created it in the mid-19th Century. The claim is that the "Moncky wrench" got corrupted to "monkey wrench." Sadly, this claim is incorrect; the wrench was around, and so named, before Mr. Moncky came along.

The true origin of the name is unknown, though if you open one up a bit and use a great deal of imagination, its head might vaguely resemble that of a primate.

—The Editors