In a long and colourful career, Lord Keen has not been afraid to cause controversy.
As a defence lawyer he represented Princess Diana's driver, Henri Paul, and alleged Pan Am bomber Al Amin Khalifa Fhimah.
In his role as the Scottish advocate general, he defended the Government during last year's prorogation trial in the Supreme Court, while he once ended up on the wrong side of the law when his penchant for shooting led him to be slapped with a £1,000 fine.
As Richard Keen QC, he took on a number of high-profile clients – but Fhima, who stood accused of 270 counts of murder in the Pan Am Flight 103 bombing trial, was perhaps his most daunting.
In 1998, the Edinburgh University-educated lawyer had an enviable reputation in insurance litigation but his skills had yet to be tested in a criminal case. He said to have walked away from the chance to defend Fhima would have been "a matter of regret" and added: "I'm pleased that I did just go ahead and do it, and I would have been pleased whatever the outcome had been."
In the end, he helped secure his acquittal.
He also defended David Cameron’s former communications director Andy Coulson, who was cleared of committing perjury in 2015.
Representing the UK Government in the Supreme Court as advocate general last year as it faced legal challenges over Boris Johnson's plan to prorogue Parliament, he told the panel of 11 justices prorogation was "forbidden territory, which is a matter between the executive and Parliament" and MPs "had the tools" to change the law if they did not like it.
Ultimately, his arguments did not wash with the judges, who ruled that the Government's actions had been unlawful.
Lord Keen's hobbies include classic cars, golf and skiing, but his passion for shooting got him into hot water.
His 12-gauge shotgun was found left out of its cabinet when police went to his Edinburgh home following reports of a suspected burglary while he was on holiday, and he was fined £1,000 for failing to secure it properly.
Ministers had hoped Lord Keen might be persuaded to stay despite tendering his resignation on Wednesday morning. But he stood firm, saying he had found it "increasingly difficult to reconcile" his obligations as a lawyer with provisions in the Internal Market Bill.