Mark T Esper, President Donald Trump's pick for new Acting US Defence Secretary, is an Army veteran who fought in the Gulf war and worked as a lobbyist for one of America's biggest military contractors.
The 55-year-old ex-classmate of Secretary of State Mike Pompeo was chosen after Acting Defence Secretary Patrick Shanahan withdrew his nomination, which took many by surprise.
Esper is taking over against the backdrop of soaring tensions between the US and Iran which has said it would surpass the uranium-stockpile limit set by its nuclear deal in the next 10 days.
Making the announcement of the new appointment, President Trump said that his current Army secretary Esper would lead the Defence Department.
"I know Mark, and have no doubt he will do a fantastic job!" he said in a tweet.
Trump told reporters that he is likely to nominate Esper for the permanent job.
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Esper, elevated from his job as Army secretary to be Acting Defense Secretary, became the third person to lead the Pentagon under President Trump. James Norman Mattis was the first one to lead Pentagon after Trump assumed office.
Esper, after graduating from West Point, served in the Army, the Army Reserve and National Guard in some capacity for more than two decades, The New York Times reported.
The NYT report said that Shanahan's 30-year career at Boeing complicated his nomination and Esper's tenure as Raytheon's top lobbyist could leave him facing a similar issue.
However, Trump has indicated that he would back Esper for the permanent job.
On Tuesday, Shanahan withdraw his nomination from the position of Defense Secretary, citing a painful and deeply personal family situation from long ago is being dredged up and painted in an incomplete and misleading way.
"The confirmation process should focus on securing our nation against threats, readiness and the future of our military, and ensuring the highest quality care and support for service members and their families," Shanahan said in his resignation letter.
Early this year, Shanahan was nominated by Trump for the position of Defence Secretary after Mattis resigned in December last year.
"After having been confirmed for Deputy Secretary less than two years ago, it is unfortunate that a painful and deeply personal family situation from long ago is being dredged up and painted in an incomplete and therefore misleading way in the course of this process.
"I believe my continuing in the confirmation process would force my three children to relive a traumatic chapter in our family's life and reopen wounds we have worked years to heal. Ultimately, their safety and well-being is my highest priority," he said.
Later, Shanahan met Esper to begin transition planning.
"The Acting Secretary will resign as Deputy Secretary of Defence effective midnight, June 23, 2019, and will conclude his service in the Department of Defence at that time," said chief Pentagon spokesperson Jonathan Hoffman.
Amidst an escalation of tensions with Iran, the US has approved the deployment of 1,000 additional troops in the Middle East for "defensive purposes" to address air, naval and ground-based threats.
Last month, the US deployed the USS Abraham Lincoln Carrier Strike Group and a bomber task force to the Middle East in response to a "number of troubling and escalatory indications and warnings" from Iran.
America has blamed Iran for last week's attacks on two oil tankers in the Gulf of Oman, an accusation Tehran has denied as "baseless.