In the Early Middle Ages (500 – 1000 AD), knighthood was granted to those who fought for the defence of the empire on horsebacks.
Later when new methods of warfare came in (people no longer fought on horsebacks) classical knights became obsolete, but the title continued in many countries.
By the 16th century, knighthood in the military context was mostly removed but it now became associated with chivalry (the combination of qualities expected of a knight, namely courage, honour, courtesy, justice, helpfulness, etc.).
So, knighthood continued to hold a sense of superiority over other classes and Sir (knighthood) became an honorific title.
Then, during WWI King George V created the Orders of the British Empire awards to reward people for their behind-the-scene services to the war effort in the UK (i.e. not on the front line).
And since then (1917), the British government has been awarding notable citizens with the Most Excellent Order of the British Empire (MEOBE).
The Order has five separate ranks: Knight and Dame Grand Cross (GBE), Knight and Dame Commander (KBE and DBE, respectively), Commander (CBE), Officer (OBE), and Member (MBE).
Achieving one of the first two ranks earns a person a slot in the knighthood, which means they can add “Sir” or “Dame” to their names, i.e. Sir Arthur Conan Doyle, Dame Judi Dench.
While non-Brits are also eligible, they only get honorary knighthood i.e. Bill Gates despite being a KBE can’t use Sir Bill Gates but can suffix KBE to his name (Bill Gates KBE).
But the monarch receives recommendations from the head of major government departments.
Awards can be made at any time but most awards are announced at either the New Year or the Queen’s Official Birthday.
While MEOBE was established in 1917, knighthood was conferred before as well, e.g. in 1705, Isaac Newton was knighted by Queen Anne — the idea was to honour a person for his/her achievements.
