Epithets

An epithet comes from the Greek word epitheton, meaning "attributed or added." It is a byname, or a descriptive term used in place of a name.

Epithets have been applied to real and fictitious people, divinities and objects. There are many epithets for the royals.

Examples have a wide range including Alexander the Great, Richard the Lionheart,  Shakespeare's Romeo and Juliet as "star-cross'd lovers," Superman is the "The Man of Steel", "The Dynamic Duo" is Batman and Robin and New York City is "The Big Apple." 

But not all epithets are so complimentary. Ivan the Terrible may have actually liked having a reputation as being terrible. Racial epithets and ethnic slurs are the ugly side of this language usage.

I'm not sure I completely agree, but one poster says that "If you know a word is either a racial slur or a racial epithet, but can’t decide which, then focus on the primary definition of the word. If the primary definition of the word has to do with racial prejudice, then it’s a racial slur. For example, the “n-word” is a racial slur. By contrast, if the primary definition of the word has little to do with racial prejudice, then it’s a racial epithet. For example, words like ape, brownie, coconut, oreo, crow, eight ball, shine, spade, spook, teapot, and, presumably, cracker, and mayo are racial epithets; not slurs."

Literary epithets are common going back to the classics. Virgil systematically called his main hero "pius Aeneas" (pius meaning religiously observant and humble) but the epithetis not always attached to the character. James Joyce uses the phrase "the snot-green sea" which is a play on Homer's epithet "the wine-dark sea."

Religious epithets are also common. Catholics, Eastern Orthodox Christians, and other Christians use epithets in the veneration of Jesus (e.g., "Christ"; "Prince of Peace"; "The Good Shepherd"), of Mary, Mother of Jesus (e.g. "Mother of God"; "Panagia").