The Klitschko brothers have been widely talked about in the media since Russian forces invaded Ukraine over two weeks ago.
The brothers, who both have decorated boxing careers, have vowed to fight for Ukraine until their dying breath.
The men were raised by their mother Nadezhda and their father Vladimir, a high-ranking military commander for the USSR.
However, a decade on from their father's death, the Klitschko brothers are now taking up arms against Russia.
The two men became involved in combat sports from an early age.
Vitali, who is now the Mayor of Kyiv, competed in boxing, kickboxing and karate, while Wladimir began his boxing training in Brovary on the outskirts of Kyiv before moving to Warsaw to work with more established coaches.
Aged just 17, Wladimir became the heavyweight Junior European Champion, and two years later, his older brother Vitali won gold at the 1996 Military World Games in Rome.
That year Vitali also graduated from his postgraduate course, a PhD in sports science, with Wladimir achieving the same qualification, earning them the boxing nicknames Dr Steelhammer and Dr Ironfist.
Both brothers have said they are "ready to die for Ukraine" as they head to Kyiv's front line as Russian troops continue their siege attempt.
Vitali and his ex-heavyweight boxing world champ brother visited a military checkpoint on the outskirts of the capital on Sunday.
Images on social media show the two being escorted around a checkpoint in bulletproof vests by Ukrainian defenders.
Russia announced a ceasefire would take place to allow for humanitarian corridors to be opened on Monday.
However, Vitali has claimed Russian troops are ignoring the fresh ceasefire as fighting continues around his city of Kyiv.
He also said a colleague, Yuri Prilipko, had been killed in shelling "while distributing bread and medicine to the people".
He added Yuri was "with the community until his last breath."
The Mayor previously told CNN Ukrainian people would continue to fight no matter how strong the Russian army is.
He said: "I am very proud to see how patriotic people are.
"We're not interested in how strong the Russian army is. We're ready to fight.
"And we're ready to die for our home country and for our families because it's our home.
"It's our future, and somebody wants to come to our home and steal our future from us."
The two former heavyweight champions also told Sky News they had already killed six people in the capital.
