Use the first name.
Some categories of personal names lack a last name–for example, some rulers and members of the nobility and many premodern people, whose name includes a place-name and not a surname (e.g., John of Gaunt).
When you list such names in your works-cited-list entry, follow the guidelines in section 2.1.2 of the MLA Handbook: omit any titles and alphabetize the name according to how it appears in the dictionary.
Thus Queen Elizabeth I would be listed under Elizabeth and Catherine of Aragon would be listed under Catherine. As always, key your in-text reference to the first element of the works-cited-list entry.
In your prose, you may refer first to the full name (e.g., Catherine of Aragon) and then, in subsequent references, to the first name alone (e.g., Catherine).
Published 2 February 2018