This is the 3999th most frequent Russian word.
кличко
"Кличко" is a surname, most notably associated with Ukrainian boxers Vitali and Wladimir Klitschko.
Here, 'Кличко' is used as a proper noun, representing the surname of a notable individual.
Кличко является известным боксёром.
Klitschko is a famous boxer.
In this sentence, 'Кличко' identifies a specific person known in the public sphere, used in the nominative case.
Сегодня на пресс-конференции выступал Кличко.
Today at the press conference, Klitschko spoke.
The usage of 'Кличко' here refers to an individual's achievements in his professional field.