For the role, Reeves spent four months learning Judo, Japanese ju-jitsu, and Brazilian jiu-jitsu from "some of the toughest guys" directors Chad Stahelski and David Leitch (uncredited) had ever encountered, which included several "LA SWAT and Navy Seal friends".

At the beginning of the film, John loses his wife Helen to a terminal illness.

Following her death, John receives a beagle puppy named Daisy, the last gift from Helen to help him cope with his grief.

While John and his new puppy are out bonding in his vintage 1969 Ford Mustang, they encounter Iosef Tarasov, the son of Russian gangster Viggo Tarasov, who tries to buy the car. John refuses to sell.

Iosef doesn't just kill John Wick's dog, as Wick expresses in possibly the fiercest monologue Reeves has ever delivered: He kills his hope, and in doing so, unleashes the full fury of a now footloose and fancy-free angel of death.

Iosef takes the Mustang to Aurelio's chop shop to have the VIN changed, but Aurelio recognizes the car and berates the Russian, punching him and throwing him out when he learns that he killed John's Dog.

VIGGO: He was once an associate of ours. They call him "Baba Yaga."
IOSEF: The Boogeyman?
VIGGO: Well, John wasn't exactly the Boogeyman. He was the one you sent to kill the f***ing Boogeyman.

Viggo tries to convince John to spare his son, but John doesn't say a word. He just hangs up the phone and gathers his guns.

Viggo sends a twelve-man hit team to John's house, but John kills them all and calls a service to professionally clean the scene.

COP: [sees dead bodies] You ... ahh ... workin' again?
JOHN: Nah. Just sortin' some stuff out.
COP: Oh, well ... I'll leave you be then. Goodnight, John.
JOHN: Goodnight, Jimmy.