Oleksiy Reznikov, who was replaced as Ukraine's defence minister on Sunday, was appointed three months before Russia's invasion and led efforts to equip Ukraine's forces with modern weaponry from allies.
The 57-year-old lawyer with little military experience, usually seen in a green fleece, has become one of the best-known faces of the country's war effort.
After helping hold back Russia's advance in the early months of the war, he spent much of his time in office galvanising support from Kyiv's allies.
Over time, he persuaded them to supply Ukraine with more and more Western-made weaponry including US Patriot air defence systems, heavy tanks and howitzers.
Most recently he led efforts to secure US fighter jets.
After the US last month authorised Denmark and the Netherlands to transfer F-16 jets to Ukraine, he wrote on Twitter that it "looks like Santa Claus does exist".
But his ministry has been beset by corruption scandals.
In January, Reznikov kept his job but his deputy was forced to resign after the defence ministry was accused of signing food contracts at prices two to three times higher than current rates for basic foodstuffs.
"The stress that I have endured this year is hard to measure precisely. I am not ashamed of anything," Reznikov said at the time, adding: "My conscience is absolutely clear."
Announcing an internal audit of procurement procedures, he admitted the ministry's own anti-corruption department had "failed" to do its job and needed to be "completely rebooted".
Reznikov was born in the western city of Lviv.
He joined the army after school and did military service in the Soviet era as a paratrooper before going to university and becoming a lawyer.
In 2004 he represented future president Viktor Yushchenko legally in his fight to overturn forged elections, securing a fresh vote that Yuschenko won.
He later became a deputy mayor of Kyiv, responsible for the hosting of the Eurovision Song Contest in Kyiv in 2017 and the UEFA Champions League Final in 2018.
From 2019 he was a member of Ukraine's delegation to the Trilateral Contact Group, negotiating with Russia and OSCE monitors in an attempt to find a diplomatic solution to end the fighting with Russia-backed separatists in eastern Ukraine.
In 2020 he joined President Volodymyr Zelensky's team and was appointed deputy prime minister responsible for reintegration of temporarily occupied territories.
He was named defence minister in 2021, with parliament approving the nomination on November 4 of that year.
Introducing Reznikov to the parliament, Zelensky said that his main task would be "to strengthen the defence capacity of the army".
Russia launched its invasion on February 24, 2022.
In his statement on Sunday, Zelensky said he was replacing Reznikov with Rustem Umerov, the head of the State Property Fund, because of a need for "new approaches".