"The tradition for most of my lifetime has been that the speaker is not a player in political debates — if he was doing his job well then you wouldn't notice him," said Jack Simson Caird, a former constitutional law expert in the House of Commons Library. "John Bercow has challenged that idea."
Bercow, 56, became a Conservative Party lawmaker in 1997 but was forced to renounce this affiliation when elected speaker 12 years later.
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It's a job older than the United Kingdom itself, stretching back more than six centuries to 1377. Bercow is the 157th person to occupy the role, sitting in the ornate chair at the center of the legislative chamber.
He earns more than the prime minister, lives in a Gothic apartment next to the clock tower informally known as Big Ben, and is the Commons representative to Queen Elizabeth II.
But Bercow is best known for his role chairing debates, where he hollers what has now become something of a catchphrase. In fact, he has said "order" an astonishing 14,000 times, according to an analysis of parliamentary records by the BBC.
His withering put-downs are delivered in such verbose, archaic language that — to the outside world watching this parliamentary sitcom — it often seems like British politics is stuck in a Dickensian time warp.
Bercow often snaps at lawmakers for "chirruping" and "chuntering from a sedentary position." In English: talking while sitting down.
In 2016, he accused one member of the government of "fiddling ostentatiously with an electronic device" and of "impairing parliamentary decorum." To translate, the government minister was on a cellphone.
He likes to address the legislators as if they are naughty school kids, once telling senior Conservative Michael Gove, "You need to write out a thousand times, 'I will behave myself.'"
There are nine lawmakers vying to succeed him, with the deciding vote coming Monday. The winner will inherit the office at a crucial time, with the U.K. headed for a rare December election that could decide the future of Brexit.
The saga has stretched the country's messy constitution to its limits. With the Conservative Party ruling despite having a minority in the Commons, Bercow has often stepped in to ensure lawmakers have a say over their nation's Brexit destiny.
Many of these lawmakers oppose a "hard" or a "no-deal" Brexit, which would abruptly sever ties to the E.U. and could cause severe damage to the economy. So Bercow giving them power to block the government has enraged those who value exiting the E.U. above all else.
This week Prime Minister Boris Johnson said Bercow had been guilty of "peppering every part of the chamber with your own thoughts and opinions like some uncontrollable tennis-ball machine."
Others however see Bercow's interventions as a good thing, making sure lawmakers are not railroaded by parliamentary convention that has historically been used to let the government have its way.
"I think the idea that the speaker as a prominent spokesperson for the democratically elected legislature is a really positive thing," said Caird, who is now a senior research fellow at the Bingham Centre for the Rule of Law, a research group in London.
Outside Brexit, Bercow was responsible for turning one of Parliament's many bars into the legislature's first nursery.
However, his former private sectary alleged last year that the speaker bullied him while he was on the team.
Bercow has also been criticized by those who say he failed to deal with wider allegations of harassment and bullying across Parliament. He denies the allegations.
Alexander Smith is a senior reporter for NBC News Digital based in London.