Roman Ratushny was a leading figure in Ukraine's pro-European Maidan movement, an anti-corruption activist who fought Russian forces with the Ukrainian army.
On Saturday, thousands of people in Kiev's Independence Square paid tribute to the "hero" who was killed in the country's east at the age of 24.
In front of the coffin draped in a yellow and blue Ukrainian flag at the foot of the monument that overlooks the sprawling square in the capital, people of all ages saluted his memory.
He had joined the army like many other civilians since the start of the Russian offensive on February 24.
"I think it is important to be here because he is a hero of Ukraine and we must remember him," Dmytro Ostrovsky, a 17-year-old high school student, told AFP.
Ratushny died on June 9 near Izium, in the Kharkiv region, where Ukrainian forces are confronting the Russian army.
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Mourners approached the body in turn, kneeling or bowing and placing a hand on the coffin where many flowers were laid.
"For all, you were a brother, for some a son, and for others a father figure," his father Taras Ratushny said into a microphone.
"Roman has always fought for the right cause and this is an example for all of us, for the young," said Hlib, a 29-year-old soldier.
Ratushny was one of the first students to protest in the Maidan (Independence) square at the end of 2013, with the location going on to be the scene of massive pro-European protests that led to the fall of pro-Russian president Viktor Yanukovych in February 2014 .
Wave of reactions
In addition to his political commitment and his fight against corruption in Ukraine, Ratushny headed the Protasiv Yar NGO, named after a historic site in Kyiv which activists sought to protect from illegal construction resulting in the destruction of a large forest in the neighbourhood.
His activism had earned him death threats.
He had appealed to President Volodymyr Zelensky and the prosecutor general in Kyiv, but no criminal investigation was opened.
"If there were 10 people like Roman in Ukraine, we would live in a completely different country," Ostrovsky said.
Earlier in the day, hundreds of people, including Kyiv's mayor Vitali Klitschko, attended the funeral at St Michael's Golden-Domed monastery in central Kiev.
"Although I didn't know him personally, I felt like a loss because when my world view was formed, (Roman) became a person who influenced my vision and the person I am now," Alina Horhol, a student who attended the funeral, told AFP.
"Roman was the kind of person who could have changed a lot in our society," she added.
The news of his death earlier this week sparked a wave of reactions on social media, including that of English football legend Gary Lineker, who tweeted: "tragic".
"Roman Ratushnyi, one of the student protesters beaten by police on the first night of Maidan revolution, has been killed fighting in the east. I interviewed him a couple of times, and spoke to him a week ago. Very sharp, bright guy," journalist Oliver Carroll tweeted.
After the tribute on Maidan square, six soldiers carried the coffin down the steps of the square through crowds massed on both sides, before lowering it into a hearse.
It was to be buried in the afternoon at the Baikove cemetery in southern Kyiv, where many prominent Ukrainian figures are buried.