Kazimierz Kazimierczak was a young boy who moved to America after his circus family was killed during an armed conflict. A traumatic accident in which his friend Janek died in an explosion in a subway led Kazimierz to kill people with no apparent reason, from which he learned to make his living by becoming a mercenary.
Time later, he was hired by numerous mob bosses, including the Kingpin, The Owl, and the leader of the "Tracksuit Mafia", to kill Clint Barton, who recently had interfered in their plans. He killed Hawkeye's neighbor, Grills as a way to harass Barton. During the man's funeral Clint and his neighbors left the building. The Clown returned to the crime scene along with the "Tracksuit Draculas" to recover any possible evidence left behind. Kazimierz was attacked by Lucky, Hawkeye's dog, but got away.
In preparation for a massive attack on Barton's building, the Clown arranged the return of Ivan Banionis, the building's former owner, to the rank of the tracksuits. The Clown and the mafia raided Barton's building, but were opposed by heavy resistance from its inhabitants. In the end, Ivan was subdued by Kate Bishop and the Clown was dealt with by Clint while the other neighbors contained the remaining tracksuits until the arrival of the police.
- 8 appearance(s) of Kazimierz Kazimierczak (Earth-616)
- 5 image(s) of Kazimierz Kazimierczak (Earth-616)
- 1 quotation(s) by or about Kazimierz Kazimierczak (Earth-616)
- 1 victim(s) killed by Kazimierz Kazimierczak (Earth-616)