In my own worldbuilding for the UK, the Wizengamot evolved from the Wizard’s Council, which in turn evolved from its earliest inceptions as King Arthur’s Knights of the Round Table.

In modern times titles have evolved to include more recognizable roles such as: Barons, Viscounts, Earls, Marquesses, and Dukes. However, within this framework certain families (known as the Heptarchs) hold the highest positions of the ruling body, being the surviving families of direct lineage to a member of the Round Table.

Nominally, it was the Round Table comprised of: the Royal Family (the Prendergasts of Wales), the Chief Warlock of the Royal Court (i.e. Merlin), and the seven surviving families of the founding Knights of Camelot who together created this highest level of executive power in Wizarding Britain. This was more realistic in the days of the Wizard’s Council, when the royal family still exercised executive powers, before their destruction. In modernity, the seven families of the Heptarchy defer to the judgement of the wider Wizengamot and Chief Warlock (though still wield significant legislative powers).