Nicknames, which occur in all cultures and time periods, play an important role in highlighting identity and provide a window into popular culture. The function of nicknames in the Middle Ages is peculiar, however, when men (as in medieval Iceland) would kill for a carelessly dropped word if it was considered to be detrimental to their honor, yet often tolerated the most demeaning nicknames. The quantity of nicknames in Old Norse literature is incomparably rich, and recurring nicknames provide a tool for understanding saga transmission, cultural history, slang, and etymology. The pool of first names was limited in Old Norse society; thus, many people were identified by not only their first names but also their nicknames. Narrative explanations of nicknames in the literature are numerous, and, although most come in the form of a brief anecdote, several examples expand on a character's biography and play a role in the shaping the plot. Such explanations of nickname origins are often also found in other sagas and medieval Scandinavian literature. Several categories of nicknames are found in Old Norse literature, such as those describing physical features, mental characteristics, and one's deeds or habits (good or bad). An alphabetic list of the nicknames from the compendium of settlers in Iceland called Landnámabók (The Book of Settlements) provides examples of the many types of nicknames and describes them in light of their linguistic origin.