Friedrich Merz, a longtime Christian Democrat and frequent intraparty critic of Chancellor Angela Merkel, is a potential front-runner to replace the German leader. 

It would mark Merz's second bid at a comeback in less than two years, after the chancellor's chosen successor, Annegret Kramp-Karrenbauer, announced that she will step down as CDU leader — and not run in the 2021 race for Germany's top job.

Merz had challenged Kramp-Karrenbauer, who is affectionately referred to as AKK by party loyalists, for the very role in December 2018.

Though the former German lawmaker has yet to declare his intention to stand for CDU leadership, Merz announced in early February that he was quitting his post at BlackRock, the world's largest investment management firm, to dig back into politics to help the conservative party "renew itself."

Read more: Could Angela Merkel's CDU make a turn to the right?

Bundestag, BlackRock Brexit

Since leaving the German parliament, the Bundestag, in 2009, Merz has taken on a number of jobs in the finance sector. In 2010, he managed the privatization of the beleaguered state bank WestLB. He is also on the board of a number of German enterprises, such as the Cologne Bonn Airport.

The 64-year-old has also held posts at various firms seeking closer ties with the US. For 10 years, he served as chairman of the nonprofit Atlantik Brücke (Atlantic Bridge) association, which promotes German-US relations. He is also a member of the Trilateral Commission, which seeks to foster cooperation among Europe, Japan and the United States.

In 2016, Merz was appointed chairman of the German operations of BlackRock. And, in November 2017, he was named honorary Brexit representative for the state of North Rhine-Westphalia.

Merkel's frequent foe

Merz had been a powerful political player within the CDU. Trained as an attorney, he served as the party's Bundestag leader from 2000 to 2002. He was in many ways Merkel's political antipode: more business-friendly and conservative — but also more provocative and entertaining.

During her ascent to the leadership, Merkel successfully dislodged Merz from the party's top echelons after a series of disputes. When the CDU and the allied Bavarian Christian Social Union (CSU) lost Germany's 2002 federal election, Merkel insisted on taking over the party's Bundestag leadership in the opposition — the position that Merz held for two years — making him her deputy from 2002 to 2004.

Merz, called a gifted orator by some, was well known for seeking to reduce complex issues to the simplest of terms. In 2004, he demanded a tax system that would permit families to calculate what they owed on the back of a beer coaster. The plan amounted to a 12% flat-rate tax on income, with a fixed rate of deduction per member of the household.

Read more: Armin Laschet is the hot contender to succeed CDU leader Kramp-Karrenbauer

Immigrants 'must conform'

Perhaps his most contentious political appeal concerned immigration and "Leitkultur." In 2000, Merz said anyone who wanted to live in the country "must conform to liberal German leading culture." The comments unleashed a wave of public debate and became a battle cry for those opposed to a multicultural society.

Merz was vehemently attacked by politicians from the laissez-faire Free Democrats and the Left party. Politicians for the Greens called him racist. Although Merkel did not agree with Merz's vision, she stood by him.

And he would remain her ardent critic. Merz's opposition to the Merkel-led grand coalition of the CDU/CSU and the Social Democrats, which governed Germany from 2005 to 2009, was seen by many as sour grapes from a political loser.

At 62, Merz attempted to jump back into politics at the very top, after having been eclipsed by Merkel in his prime. He lost his 2018 campaign for CDU party leader to Kramp-Karrenbauer in a 517-to-482 vote.

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