Jeremy Corbyn was the break-out candidate who defied all the odds to upend the Labour establishment.
The veteran rebel was put forward for the leadership by fellow left wingers as it was seen as “his turn” to stand, with seemingly little hope of success, after Ed Miliband quit in the wake of taking the party to defeat in 2015 against David Cameron.
But something unusual happened, Mr Corbyn appeared to catch a mood on the centre left as Labour members insisted they needed a more “genuine” leader.
The opposition to the Corbyn surge was also fractured when neither Yvette Cooper or Andy Burnham was willing to stand down to try and blunt the rise of the Corbynistas.
The result was that in September 2015, Mr Corbyn romped home on the first ballot with a commanding 59.5% of the vote.
The bulk of the parliamentary Labour Party was perplexed at the turn of events, the majority of the rapidly swelling membership was delighted.
Tensions
Tensions soon exploded over the June 2016 Brexit referendum.
Critics accused Mr Corbyn of not taking the situation seriously enough, and polls showed that 40% of Labour supporters did not know where their party stood on the key issue as the closely fought referendum loomed into view.
In the aftermath of the surprise Brexit vote, Mr Corbyn faced a shadow cabinet rebellion led by then foreign affairs spokesman Hilary Benn.
Mr Corbyn moved quickly to sack the son of former left wing standard bearer Tony Benn, which led to a mass exodus from the shadow cabinet.
The Labour leader refused to be bowed, and appointed supporters to fill the vacant spaces as he saw off a challenge to his leadership by Owen Smith, increasing his backing among party members in the process with 61.8% support in the contest.
Mr Corbyn was re-elected Labour leader with a bigger mandate than before, and then faced Theresa May’s snap general election in June 2017.
Despite some early polls putting Labour more than 20 points behind the Tories, the party received its biggest election upsurge since 1945 and helped deprive Mrs May of a Parliamentary majority.
Electoral boost
Mr Corbyn used the electoral boost to solidify his position, but continuing controversy over the way Labour was dealing with anti-Semitism allegations among members dogged the party.
The Labour leader tried to walk a tight rope on Brexit in the run-up to the snap December 2019 general election, insisting he would seek new terms on EU membership, but refusing to say which option he would back in a subsequent referendum.
Boris Johnson’s blunt “get Brexit done” message smashed all before it, and Mr Corbyn’s hopes of a socialist victory were left buried under the collapse of Labour’s so-called “red wall” in Wales and Northern England.
He announced he would quit as leader, but even centrist would-be successor Sir Keir Starmer, acknowledges Mr Corbyn has turned the party’s political dial to the left.