Question: John Will completed his blackbelt under one of these men, a brother renowned for his BJJ skills?

Context paragraphs:
Hélio Gracie: Hélio Gracie (] ; October 1, 1913 – January 29, 2009) was a Brazilian martial artist who, together with his brother Carlos Gracie, founded the martial art of Gracie jiu-jitsu and with Luiz França and Oswaldo Fadda the martial art of Brazilian jiu-jitsu (BJJ).  According to Rorion Gracie, his father Hélio is one of the first sports heroes in Brazilian history; he was named Man of the Year in 1997 by the American martial arts publication "Black Belt" magazine.  A patriarch of the Gracie family, he was the father of Rickson, Royler, Royce, Relson, and Ultimate Fighting Championship (UFC) co-founder Rorion Gracie, among other sons and daughters.

Jean Jacques Machado: Jean Jacques Machado is one of the five Machado brothers, including Carlos, Roger, Rigan and John, renowned for their Brazilian Jiu-Jitsu (BJJ) skills.  Nephews of BJJ co-founder and Master Carlos Gracie, the brothers learned the martial art from an early age.

Filippo Negroli: Filippo Negroli (ca. 1510–1579) was an armourer from Milan.  He was renowned as being extremely skilled, and may be considered the most famous armourer of all time.  Working together with his younger brothers Giovan Battista (ca. 1511-1591) and Francesco (ca. 1522-1600) in the Negroli family workshop headed by their father Gian Giacomo Negroli (ca. 1463-1543), Filippo was specialized in repoussé of armour, whereas his brother Francesco was renowned for his damascening skills.  Filippo's pieces are considered especially remarkable because they were wrought in steel, rather than the more-easily worked iron that was the traditionally assumed medium.

Melbourne University Law Review: The Melbourne University Law Review is a triannual law journal published by a student group at Melbourne Law School covering all areas of law.  It is one of two student-run law journals at the University of Melbourne, the other being the "Melbourne Journal of International Law".  Students who have completed at least one semester of law are eligible to apply for membership of the editorial board.  Applicants are assessed on the basis of their performance in a practical exercise, academic aptitude, proofreading skills, editing skills and enthusiasm.  The 2017 editors-in-chief are Jordonne Colley, Chenez Dyer Bray and Marcus Roberts.

Ricardo Migliarese: Ricardo “Animal” Migliarese (aka Rick Migliarese, born December 17, 1978) is an American born professional Brazilian Jiu Jitsu grappler and a 4th degree Relson Gracie Brazilian Jiu Jitsu Black Belt with approximately 20 years of experience in BJJ and Mixed Martial Arts.  A World and Pan-Am Champion, Rick is a trainer, training partner and coach to UFC and MMA fighters as well as other World and Pan-Am Champions.  He currently lives in Philadelphia, PA where he teaches at Balance Studios which he co-owns with his brother, Phil Migliarese.  Rick is also one of the co-founders/co-owners of Matrix Fights Promotion Company.

Carlos Gracie: Carlos Gracie (September 14, 1902October 7, 1994) was a Brazilian martial artist who is credited with being one of the primary developers of modern jiu-jitsu in Brazil.  Along with his younger brother Hélio Gracie and fellow students Luis Franca and Oswaldo Fadda, Gracie helped develop Brazilian jiu-jitsu (BJJ) based on knowledge from Mitsuyo Maeda, and is widely considered to be the martial-arts patriarch of the Gracie family.  Carlos Gracie acquired his knowledge of Jiu-Jitsu by studying in Belem under Maeda and his students.  As he taught the techniques to his brothers, he created a martial arts family with Hélio and with other members of the Gracie family who provided key contributions to the style.

John Will: John Will (born (1957--)16 1957 ) is a notable martial artist from Australia.  Will won the "Best Exponent Award" in the first World Silat Championships held in Jakarta in 1981.  Will also completed his black belt in Brazilian Jiu Jitsu under Rigan Machado and his brothers, John, Roger and Jean Jacques Machado in 1997; making him one of the first twelve foreign nationals to have earned a black belt in Brazilian Jiu Jitsu.

Leandro Vieira: Leandro Vieira is a Brazilian Jiu-Jitsu instructor and competitor and a co-founder, leader and fighter for Checkmat BJJ.  He is also the Brazilian Jiu-Jitsu head coach for the MMA team at American Kickboxing Academy, renowned for being one of the best MMA teams in the world.

Technician fourth grade: Technician Fourth Grade (abbreviated as T/4 or TEC4) was one of three United States Army technician ranks established on January 8, 1942 during World War II.  Those who held this rank were often addressed as Sergeant.  Technicians possessed specialized skills that were rewarded with a higher pay grade.  These skills could be directly related to combat, such as those skills possessed by a tank driver or combat engineer, or skills possessed by those in support functions such as a cooks or mechanics.  Depending on his or her function, he or she might be called upon by an officer to command a group of men for a specific task.  They were non-commissioned officers, as were sergeants.  Initially, they shared the same insignia but on September 4, 1942, the three technician ranks were distinguished by a block "T" imprinted below the standard chevrons.  Unofficial insignia using a technical specialty symbol instead of the T were used in some units.

March Madness pools: March Madness pools are a form of sports betting based on the annual NCAA Division I Men's Basketball Tournament each spring in the United States.  The increasing interest in this event is fostered by March Madness pools, or brackets.  A bracket is a form that can be completed on-line or printed out and completed by hand whereby the participant predicts the outcome of each game in the tournament.  His or her predictions are compared against others in the pool, and whoever has the best prognostication skills wins the contest.

Supporting paragraphs: John Will Jean Jacques Machado
Answer: Jean Jacques Machado