The king consort (female: queen consort) sometimes arrives with, and is always the spouse of, the monarch (queen or king). The king consort has no room requirements and does not show up on the nobles screen. He does not perform any meaningful function (other than producing children), and makes no mandates or demands. Although he can be assigned all labors, this is apparently a bugBug:3721. The king consort cannot be appointed or replaced.
Because there can only be one monarch, under normal conditions there can only be one king consort. However, it is possible to have no consort; this occurs when the monarch is not married (or, in more severe cases, when the monarch no longer exists).
Interestingly, the plural form of king consort is not the obvious "king consorts", but rather "kings consort". This is because the "consort" serves as an attributive adjective and not a nominal portion of the noun phrase.
The female equivalent of a king consort is a queen consort, who arrives with and is always the wife of a king. She always has the profession "queen consort" unless she has a custom profession title. Aside from the naming (and, of course, the gender), the king consort and queen consort are completely identical.
The naming of king or queen consorts can be confusing; the king consort is always the husband of the queen and the queen consort is similarily always the wife of the king.
 Fortress Mode
In Fortress mode, the king consort can arrive along with the monarch. This dwarf is always a historical figure, and so can possibly be a night creature. Through a mountainhome's evolution, the consort can change or disappear many times. The consort is not listed in the obles screen, although he is otherwise considered a noble.
As a historical figure, the king consort is also eligible to arrive without the spouse. This may or may not be a bugv0.34.07.
The king consort will be displayed in thenits screen as having the job "Noble" in purple text, but he will not have the distinctive purple colour characteristic of all nobles. Instead, he appears as the colour of his highest profession in both the units screen and the display.
When the cursor on the units screen is placed over the king consort's name, the foreground of the name becomes purple (similar to most nobles), but otherwise keeps the colour of his profession (similar to the militia commander). This suggests that the game may treat kings consort sometimes as nobles and sometimes not. Whether this has any effect on noble-specific thoughts is unknown.
Interestingly, the king consort has the exact same precedence as the monarch. This means that no other noble status will override the status as a king consort, with the obvious impossible exception of also being the king. This has no effect on anything but the titles this unit receives and its display in various screens.
Although the king consort does not himself have room or furniture requirements, like all married dwarves the king consort shares a bedroom with his spouse, in this case the monarch. Because of this, the king consort can enjoy the royal bedroom prepared for the monarch without any extra furniture or value improvements.
If the king consort dies, then no new king consort can be appointed until the monarch herself is removed from power. This is because dwarves will never remarry.
On the other hand, if an unmarried queen marries a dwarf, that dwarf will become king consort provided that he does not have a more important noble status. Forced socialization can be used to cause this.
If the current monarch dies, then the consort will also be replaced or removed based on the marital status of the heir that assumed the throne. In some cases, no heir, or an heir not present at the fortress, may exist to assume the throne. When this happens, the position of king consort will simply cease to exist. The exact mechanism of selecting an heir is not yet well known, so it is not feasible at the moment to select the king consort by arranging unfortunate accidents for the queen.