Answer: Exclamation mark
Exclamation marks were introduced in the 15th century by printers who were looking for a way to denote a sense of wonders, admiration or exclamation with a punctuation mark. The land itself is believed to be derived from Latin io which was an exclamation of joy. Over time, "I" was placed over "o", "o" shrunk in size, and by the time the printers adopted the symbol, they simply stylized the shape of it. The label remains in continuous use, but with variations in meaning and use ever since. Despite its long user history, it was only a hundred years after the typewriter's introduction that the exclamation point received a dedicated key.
Prior to the mid-1970s, printers wishing to insert an exclamation mark in their text were forced to enter a period, hit the backspace key and strike an apostrophe during the period to form a provisional exclamation mark.
Bonus Keyboard Trivia: Other characters historically called axes of typewriter designers include the numbers "One" and "Zero". Early printers used lowercase letters L and uppercase letter O to denote 1 and 0.