K-1 - The Seido Kaikan Karate Commercial Event

According to Wikipedia,
K-1 is a combat sport that combines stand up techniques from Muay Thai, Karate, Savate, San shou, Kickboxing and traditional Boxing to determine the single best stand-up fighter in the world (the "1").

And refered to non-official K1 site www.k-1.co.za
K-1 Definition:

Martial arts competition: a sport in which competitors utilize standing techniques from sports such as karate, kick-boxing, kung fu, and tae kwon do to determine the world's strongest martial arts.

The sport was first formed by Kazuyoshi Ishii, a former Kyokushin karate practicioner who had formed his own organization, Seido-kaikan karate, in 1980. Seido-kaikan arranged several successful challenge events against other martial arts organizations, originally using rules based on the Kyokushin Knockdown karate rules, but gradually adapting and changing closer to kickboxing rules. In 1993 Mr. Ishii founded the K-1 organization exclusively as a kickboxing organization, closely cooperating with, but independent from Seido-kaikan.

Later K1 Competition Event also known to gave birth to big name such Andy Hug and Francisco Filho, who was first being popular in kyokushin atmosphere.

For now, Seido Kaikan's K1 is known as one of the most rich Martial Art Organization. The head structure of K1 Organization now taken by Sadaharu Tanigawa as The President and Nobuaki Kakuda as The Executive Producer.

FYI, Nobuaki Kakuda formerly known as one of the most popular referee in K1 Martial Art Competition. He also ever being a Contestant on the K- 1 event. One of the his most popular battle is between him againts Andy Hug, one of the Kyokushin and K-1 Legend. osu!