Ampersand isn’t a letter, it’s a character that comes from the Latin word et, which means and. Over time, the scribal hands that recorded these ands grew to think they should connect to form a ligature. While this practice dates back to first century Rome, the name ampersand did not gain popular use until the early 19th century.
Ampersand set in Williams Caslon by William Berkson reads Et to my eye with a kind of extravagance you’ll not find elsewhere in the Caslon Roman. Beautiful to think that these ‘fleurons’ could just be waiting for you in the middle of a block of text.