Sajid Javid is the son of a Pakistani immigrant bus driver who fought racism to become a high-flying banker and eventually Boris Johnson's finance minister before unexpectedly resigning on Thursday.

The 50-year-old's career had been skyrocketing until he became the biggest casualty of Johnson's first government shakeup since the Conservative leader became prime minister in July.

Javid served as interior minister under former prime minister Theresa May and was chosen by Johnson to become his effective second in command just as Britain was facing a crash exit from the European Union.

He replaced Philip Hammond as Chancellor of the Exchequer when the prospects of a messy divorce after 46 years was unnerving the markets and sending the pound to multi-year lows.

Yet the father of four, who was born in Rochdale, near Manchester, and fondly recalls once shaking free market champion Margaret Thatcher's hand as a young boy, already had first-hand experience navigating financial turmoil.

Javid made big bets and huge profits as a risky derivatives trader for Deutsche Bank during the 2008-2009 global financial crisis.

Javid then entered politics and saw his ministerial career swing from one high to the next.

Economists viewed him as a liberal who was fluent in complex banking matters and knew the drawbacks of bureaucracy and red tape.

Javid's instincts saw him vote in 2016 to remain in the European Union because of its economic benefits to trade.

But he later rallied to the Brexit cause and ended his own Tory leadership challenge to support Johnson.

Breaking barriers

Javid grew up in a tough area of the southwestern English city of Bristol, where he recalled being called the racist term "Paki" in school.

He also faced initial questions about his background in his early days in finance but persevered and became the first from an ethnic minority in one of the top three British government jobs.

He won promotions to business and then housing secretary before arriving in April 2018 at the interior ministry.

Javid developed a reputation as a loyal minister who was tough on crime but also sensitive to the racial injustices of Britain's past immigration policies.

His predecessor quit amid a scandal over the "Windrush" generation - Britons born in the Caribbean who migrated legally in the 1960s but were being deported because of a lack of papers.

His first pledge was to promote "decency and fairness".

But he faced criticism for cancelling the UK citizenship of Shamima Begum - a 19-year-old mother who as a teen to join the Islamic State Group in Syria and wanted to return to London.

Javid's appointment as finance minister was in keeping with Johnson's pledge to create a diverse cabinet.

His wife Laura is a church-going Christian and he is not a practising Muslim himself. Some of his four children are looking at future careers in finance.

Javid's biggest challenge was finding a balance between his free market views and the high-spending pledges Johnson made during his campaign.

Johnson had also pledged to cut taxes - two incompatible promises if Britain was to keep to strict budget rules.

Javid's seven-month stint as finance minister was rocked by rumours of deep division's with Johnson's chief political adviser Dominic Cummings.

"The prime minister said he had to fire all his special advisers and replace them with Number 10 special advisers to make it one team," a source close to Javid told Britain's Press Association.

"The chancellor said no self-respecting minister would accept those terms."