A Japanese judoka, prizefighter, and former member of the Kodokan named Mitsuyo Maeda emigrated to Brazil in the 1910s where a local influential businessman named Gastão Gracie helped him get established. In return for his aid, Maeda taught judo to Gastão's son Carlos, who then taught the art to his brothers, including Hélio Gracie. Through their own study and development, Carlos and Hélio are regarded as the originators of Brazilian Jiu-Jitsu as a style distinct from Judo.
Brazilian Jiu-Jitsu became internationally prominent in the martial arts community in the 1990s, when Brazilian Jiu-Jitsu expert Royce Gracie won several single elimination martial arts tournaments called Ultimate Fighting Championships against sometimes much larger opponents who were practicing other styles.
Brazilian Jiu-Jitsu inherited its emphasis on using leveraged counterpoise, and the opponent's own weight, as well as a majority of its technique from Kodokan Judo. However, there has been considerable divergence since that time as Brazilian Jiu-Jitsu evolved. Some argue that the differences are more in culture and moral goals than in the physical principles and techniques of the two arts.
The main difference is that Judo, especially in its Olympic sport form, emphasizes throws, while Jiu-Jitsu emphasizes submission of the opponent using joint locks or chokes. Judo has a much higher amount of referee intervention; in Judo matches, the competitors are often returned to the standing position, while in Jiu-Jitsu matches, the participants are generally allowed to remain on the ground while working for a submission.
Contributing factors to the divergence include the Gracies' desire to create a national martial art, the influence of Brazilian culture, the non-participation of the Gracie schools in sport judo, the post World War II closing of the Kodokan by the American Occupation Authority (which were only allowed to reopen on the condition that emphasis be shifted towards sport), as well as the Gracies' own additions to the body of technique and opinions regarding self-defense, martial arts and training methods; and, more recently, the influence of mixed-martial-art competitions such as the Ultimate Fighting Championship.
Kimura BJJ's Nate Chandler, just 8 years old, competed on November 19th in The Good Fight 'Thanksgiving Throwdown' in Farmington, CT. Nate weighed in at 54 lbs and competed in 8 fights, winning 6 times in both Gi and No-Gi divisions. Impressively, the only person in Nate's weight class was a Green belt (two belt levels above yellow belt Nate), who Nate beat 4 times on his way to two gold medals.