Centuries ago, British Royals were the ones who ruled Great Britain. Although the "Houses of Parliament" (or something like that) already existed since 1257, the members who represented the "shires" were never much more than advisors to the King or Queen. He or She was the one who had the final decision if taxes were raised, a war was declared to another country, or a maid at the court was allowed to marry. There were important "Secretaries of State" or "Chief Ministers" (Henry VIII´s Thomas Wolsey, or Elizabeth I´s Sir William Cecil among others), but they weren´t as powerful as they became later.
This changed when Queen Anne died without a heir in 1714, and George I.became King. He was related to the Tudor´s and the Stuart´s, who supplied the Royals between 1485 and 1714 (among them the mentioned King Henry VIII and Queen Elizabeth I), but didn´t speak English, being born in Osnabrück, Germany. As George I also ruled a part of what is now Germany, he needed someone powerful who could represent him and his politics when he was away.
From 1714-17 and 1721-42, Whig-politician Sir Robert Walpole
(1676-1745) became "First Lord of the
Treasury" and from 1721 on was regarded as the first "Prime Minister" in
British history, although he himself rejected the title. Another sign from
today´s point of view that he was the first "non-Royal" politician
(leaving Oliver Cromwell out) who ruled Great Britain is that he was the
first one who resided in "10, Downing Street" since 1732, which is the home
of the Prime Minister until today.
Walpole,
you can see a signature from him from 1725 (a part of a document), was able
to stay almost untouched during several crises. His home near the "Houses
of Parliament" enabled him to be there whenever his presence was needed (or
political rivals were too far away for debates). He led almost like a monarch,
and when George I died in 1727, he had become too important and remained
in office when George´s son became king George II (until 1760).
Although the next King, George III (grandson of the II), tried to get back the power which was held by politicians, he had to learn that the times of "all-power" of the monarchy were over.
With Sir Robert Walpole, a new age had begun.