Formal surnames attached to a family are a later invention than aristocratic titles. In fact, surnames were originally introduced for the sole purpose of identifying individuals for the purpose of taxing them. When the English tried this on the Welsh, they mass rebelled by all choosing the name "Jones."

This was especially the case for commoners, or non aristocrats, who only had first names, and had to be uniquely identified by their professions, the names of their fathers or a well known relative. If Bob the Builder got a knighthood for exceptional diligence in building siege engines for the noble and perennial cause of annoying the French, then the only real name the title could be attached to would have been "Bob."

The reason it is different for other titles is that those titles belonged to the landed aristocracy, and were generally titles to the fiefdoms of that territory, so titles like Lord Acton, Lord Dunsany, or Alfred, Lord Tennyson, referred to actual places. If a higher title is awarded to a commoner who does not possess a hereditary fiefdom, then a fiefdom will be invented for them such as when William Thompson became Lord Kelvin.

Along similar lines, the name of the famous renaissance polymath Leonardo da Vinci is "Leonardo". He was born in the city of Vinci, so calling him "Leonardo from Vinci" was an easy way of distinguishing him from the other Leonardos around. Nobody during his lifetime would have addressed him as "Da Vinci".

By the same token, it is strange that one of the pioneering visionaries of computing is commonly known as Ada Lovelace, even though her actual surname was 'King' (née Gordon) Her full title was 'Ada King, The Right Honourable The Countess of Lovelace,'

It's one of those "how important is the title" things. According to an article in the workplace magazine at a (now very) former workplace, to celebrate the honours doctorate of Princess Christina, her full title (with doctorate) would be "Princess Christina, Dr Mrs Magnusson".

The explanation given is that the princesshood attached to her, personally. I suspect it is the same with a knighthood. And the "dr" comes before the "mrs", as it is more prestigious.

But, as with many things, don't think TOO hard about it.

https://en.wikipedia.org/wiki/Princess_Christina,_Mrs._Magnu...

What I didn't know is if you are knighted, you have to give up your birth citizenship.

Foreigners get honorary knighthoods: Bill Gates, Steven Spielberg, Dwight Eisenhower etc. Apparently if you take up British Citizenship it automatically converts.

That seems to be a US rule [1], not a condition imposed by the knighting jurisdiction. Maybe some other countries have similar no-titles rules, but I couldn't find any (might be searching for the wrong terms).

[1] https://en.wikipedia.org/wiki/Foreign_Emoluments_Clause

Well, a knight is a servant to the monarch, thus subject of her.

Knighthood is not just a title, it also means you are servant, subject to the monarch. My understanding is you have to become citizen for this.

And while Britain allows dual citizenship, most countries do not. So in most cases you need to rescind your other citizenship in order to be come an actual knight.

Not quite true. If you wished to be addressed by the title of 'Sir' or 'Dame,' you would have to be a British citizen, but a non citizen can add letters after their name, e.g. Bob Geldof, KBE, remains a citizen of the Republic of Ireland.

I believe Commonwealth citizens (at least, those from countries that share a monarch with the UK) are entitled to use 'Sir' or 'Dame' as well: though Canada, for one, seems to take a dim view of its citizens accepting British honours.