Answer by Garrick Saito:
, the founder of Kyokushin kaikan, a full contact form of karate, is well known in karate circles for having killed over 50 bulls with his bare hands, three of which are purported to have been done with a single blow. He considered it a test of the strength of his karate.
While not combat "to the end," he is also famous for his 100-man kumite, a test of technical proficiency, physical endurance and mental stamina. This involved sparring one man, one after another, a feat only a handful of men in history can say they've completed. Most failed due to physical exhaustion.
Not expecting anything more from his students that he himself was not willing to do, Oyama completed the 300-man kumite, fighting 100 men per day over a period of three days. No man, except Oyama, has ever been able to claim this accomplishment.
The test Mas Oyama visualized for kyokushinkai would require far more than technical proficiency. It would demand that the individual who accepted the challenge be at the peak of his abilities. Physical endurance, strength, and mental stamina would have to be tantamount. Physiological functions would have to be at their peak. Kokoro – heart, mind, and body – would have to be united as one. Oyama chose hyakunin kumite (100-man fighting) as the ultimate test for kyokushin students. His decision to use this came after careful study of other martial arts and what they employed as their ultimate test. A 19-century kenjutsu master, Yamoka Tesshu, performed hyakushin-tachi, or "100-man challenge." Tesshu, in 100 consecutive duels, victoriously fought opponents with the shinai (bamboo sword). Mashiko Kimura stands alone as the predominant athlete in judo, for no other practitioner of the art has ever accomplished the hyakushin-nage or "100-man throws." As friends, Oyama admired Kimura for his intense training methods that were similar to his own. Over a period of two consecutive days, Kimura accomplished the hyakushin nage. These two 100-man fighting ordeals were the factors in Oyama's choice of hyakunin kumite for kyokushin's ultimate test.
100 Fights in 3 Days
Oyama would not require anything of his students that he had not previously done. Therefore, Oyama would elect to undertake the 100-man fighting first. It was soon after his arduous training in the mountains when Oyama chose hyakunin kumite as the ultimate test for kyokushin. He was at the pinnacle of physical conditioning and believed there was no better time to take on such a task. Therefore, he selected the best black belt students from his dojo for his opponents, and he required each student to fight him for two minutes, consecutively. After the entire group of students fought Oyama, they repeated their fighting rotation until 100 bouts were complete. To satisfy Oyama's personal supreme test, he chose to face 100 consecutive fights a day over the course of three days, for a total of 300 fights. He would take small breaks after every 20 or so fights in order to replenish fluids and tend to matters of personal hygiene. Sleep between each of the 100 man fight days was at a minimum for Oyama due to the increase of adrenaline and anticipation of the next day's fights.
Many of the students who faced Oyama fought three or four times during the three days. Several students could only face him once due to injuries they sustained. Oyama would knockout many students with a single blow. Although he wanted to continue for a fourth day, he was unable to because of the lack of willing opponents. For these three days, Oyama fought full-contact, without pads, against his top students, defeating them all. No other martial artist in history has even made an attempt at duplicating his 300-man fight. And because of the punishing effect this ordeal had on his students, Oyama would not attempt such a feat again.
A good biography is here.