I just read that John of Gaunt was "the first of the Lancasters." It was in Daughter of Time, but I'm assuming it's factual. My question: How does someone become the first of a house like that? I always thought of them like families, that don't really have a "first." Especially since they seem to feud with each other, why would there be more? Please enlighten, thanks.
When discussing royal houses which were not the main house, there are no really concrete rules about who is "first" or even what makes up such a house.
However, there are some rules of thumb when it comes to a situation like John of Gaunt and the Lancasters.
The first thing to note is that the Lancastrian house is what is known as a "cadet" branch of the royal family (which was at that time the House of Plantagenet). Many of the most important "Houses" we talk about were cadet branches of a main house.
There have been many such cadet branches in history which have played an important role in various monarchies. The Lancastrians, of course, were just one such. The Yorkists and even the Tudors also counted.
How a cadet branch is created can be formal or informal, but most commonly happens when a son of the monarch who is not the heir apparent/presumptive starts their own influential line. The name usually tends to follow the title of the founder at the time or is some sort of hyphenated addition to the main house name.
For instance, John of Gaunt was third son of Edward III, and Duke of Lancaster and this was the main title his branch held. Hence, he founded the House of Lancaster. The House of York was founded by Edmund of Langley, 1st Duke of York and fourth son of Edward III.
It is important to note here that since the Western world overwhelmingly used male-preference inheritance, cadet branches would almost always be created by sons who had enough clout to form their own important families. Any daughters who were married would be considered to have married into an existing house because property, titles, and hence power, would be passed in the male line.
So, we should be aware that Edward III's second son, Lionel of Antwerp, Duke of Clarence would have had a house, but he only sired a daughter, Philippa, and this ended any sort of House of Clarence almost immediately.
Female-founded houses exist, but are more common for female rulers of the main house where it was considered desirable for the name of the royal house to remain the same or similar for continuity reasons.
We see this in more modern times with Maria Theresa of Austria (and her husband Francis Stephen, Duke of Lorraine) founding the House of Habsburg-Lorraine. Also, the contemporary Queen Elizabeth II maintaining the House of Windsor name, despite not only having married, but also married a man (the former Prince Phillip of Greece) who had a claim to some house membership himself.
This is alluded to in the names of her descendants in the male line without a royal title being declared to have the surname of Mountbatten-Windsor, while the house name remains Windsor.
For cadet branches, maintaining the male line is the most important feature of the house, and so few, if any such special cases, are made for female members.
When those do happen, they are usually either to keep an old, prestigious name alive where it would have otherwise died out, or to ensure that certain lands remain in that family due to specific inheritance requirements.
Let's move on to a very important point about how Houses affect history in our second point.
The second thing to note is that a cadet branch could technically exist for every non-heir offspring of a ruler who has offspring themselves, but more popular history really only follows those branches that became influential or remarkable for some reason.
For instance, the House of Orleans, which was very important in 17th-19th Century France was founded by Philippe I, Duke of Orléans who was the brother of Louis XIV. Philippe was the only brother of Louis, but Louis himself, as well as his successor Louis XV had a number of children who did not end up founding a house.
In the sad case of Louis XIV, this is mostly because all his male children (and grandchildren) predeceased him.
In the cause of Louis XV, however, there were a number of sons in addition to Louis Auguste (the future Louis XVI). Those other sons, since they became King in their own right or were otherwise unremarkable, and did not form what historians would really call their own cadet branches.
In light of this, the Orleanist cadet branch held some particular importance. The Duc d'Orleans was Regent for Louis XV, and consequently had a great deal of power in the Regency period in the early 18th Century.
And while the main line of the Bourbons (themselves a previously a cadet branch of the royal House of Valois) was truncated first by disease and then by Revolution, the Orleans rulers were perennially waiting at the edges with their strong claim to the throne if their royal Bourbon cousins finally either died out or were ultimately overthrown.
History tells us that in that case, they did get their chance with King Louis-Phillippe who succeeded Charles X after the Revolution of 1830. Unfortunately for them, the Orleans house itself was overthrown in 1848. A disappointing end for the Orleans family that had been waiting and even scheming for their opportunity for over a hundred years.
So, to unify what is being talked about there are two things to bear in mind:
A historian who may dive deeper into the specifics of a certain area is bound to recognize more houses than those of us who have just learned about certain houses in a textbook or general studies. Those houses may well have considered themselves to be part of a particular house, or the historians might simply assign them to a "house" for ease of tracking their relatives down the years. Where a Lancastrian house member might have their rose badge and keen awareness of their house membership, there might be less of a "brand" out there for less important, but still quite valid houses that you never hear about.