Wisaksil Wangek (Thai: วิศักดิ์ศิลป์ วังเอก ; born December 8, 1986), better known as Srisaket Sor Rungvisai (ศรีสะเกษ ศ.รุ่งวิสัย), is a Thai professional boxer.
 He is a two-time WBC super flyweight champion, having held the title since March 2017, and previously from 2013 to 2014.
 As of September 2017, Sor Rungvisai is ranked as the world's best active boxer in the division by the Transnational Boxing Rankings Board (TBRB) and BoxRec, and second by "The Ring" magazine.
 BoxRec also ranks him as the world's fifth best active boxer, pound for pound, and tenth by the TBRB.
Timothy Ray Bradley Jr. (born August 29, 1983) is an American former professional boxer who competed from 2004 to 2016.
 He held five world championships in two weight classes, including the WBC light welterweight title twice between 2008 and 2011; the WBO light welterweight title from 2009 to 2012; and the WBO welterweight title twice between 2012 and 2016.
 In October 2013, "The Ring" magazine ranked him as the world's third best active boxer, pound for pound.
 Bradley is particularly known for his trilogy of fights against Manny Pacquiao, whom he fought in 2012, 2014, and 2016.
Guillermo Rigondeaux Ortiz (] ; born September 30, 1980) is a Cuban professional boxer.
 He has held multiple world championships at super bantamweight, including the WBA (Super) and lineal titles since 2013, and previously the WBO and "Ring" magazine titles between 2013 and 2016.
 As of May 2017, Rigondeaux is ranked as the world's best super bantamweight by "The Ring", the Transnational Boxing Rankings Board, and BoxRec; "The Ring" also ranks him as the sixth best active boxer, pound for pound.
Héctor Manzanilla Rangel (born June 28, 1985 in Los Teques, Miranda) is a Venezuelan bantamweight boxer who has won a bronze medal at the Central American Games.
 He is most respected for giving amateur superstar Guillermo Rigondeaux one of the toughest fights of his career.
Gennady Gennadyevich Golovkin (; born 8 April 1982), often known by his nickname "GGG" or "Triple G", is a Kazakhstani professional boxer who currently holds the unified WBA (Super), WBC, IBF, and IBO middleweight titles.
 As of September 2017, he is ranked as the world's best middleweight by BoxRec and the Transnational Boxing Rankings Board (TBRB), and second by "The Ring" magazine.
 He is also ranked as the world's best active boxer, pound for pound, by "The Ring"; second by the TBRB; and third by BoxRec
Chad Dawson (born July 13, 1982) is an American professional boxer.
 He is a three-time former light heavyweight world champion, and was one of the most highly regarded boxers in that division from 2006 to 2013.
 Dawson rose to prominence on the world stage in 2007, when he defeated Tomasz Adamek to win the WBC light heavyweight title.
 After vacating that title, he defeated Antonio Tarver in 2008 to win the IBF and IBO titles.
 Dawson's first career loss was to Jean Pascal in 2010, after which he would win the WBC title for a second time, as well as the "Ring" magazine and lineal titles, by defeating Bernard Hopkins in 2012.
 In the same year, "The Ring" ranked Dawson as the world's tenth best active boxer, pound for pound.
Tyson Luke Fury (born 12 August 1988) is a British professional boxer.
 He has held the "Ring" magazine heavyweight title since 2015, after defeating long-reigning world champion Wladimir Klitschko.
 In the same fight, Fury also won the unified WBA (Super), IBF, WBO, IBO and lineal titles, with the victory earning him Fighter of the Year and Upset of the Year awards by "The Ring".
 Fury was subsequently stripped of the IBF title later that year for being unable to grant a fight against their mandatory challenger, Vyacheslav Glazkov, due to agreeing to a rematch with Klitschko.
 In 2016, Fury vacated the WBA, WBO, IBO, and lineal titles following an ongoing medical investigation and personal issues and two cancellations of the Klitschko rematch.
 In August 2016, Fury was ranked by BoxRec as the world's sixth best active boxer, pound for pound.
Andre Michael Ward (born February 23, 1984) is an American former professional boxer who competed from 2004 to 2017.
 He retired with an undefeated record and held eight world titles in two weight classes, including the unified WBA (Super), WBC, "Ring" magazine, and lineal super middleweight titles between 2009 and 2015; and the unified WBA (Undisputed), IBF, WBO, and "Ring" light heavyweight titles between 2016 and 2017.
 During his reign as light heavyweight champion, Ward was ranked as the world's best active boxer, pound for pound, by "The Ring" magazine and the Transnational Boxing Rankings Board (TBRB), as well as the world's best active boxer in the division by "The Ring", the TBRB, and BoxRec.
Sergey Alexandrovich Kovalev (Russian: Сергей Александрович Ковалёв ; born 2 April 1983) is a Russian professional boxer.
 He is a former unified light heavyweight world champion, having held the WBA (Undisputed), IBF, and WBO titles between 2013 and 2016.
 "The Ring" magazine named him their Fighter of the Year in 2014, and in July 2016 he was ranked as the world's best light heavyweight by "The Ring" and BoxRec; both of which also ranked him as the world's third best active boxer, pound for pound.
 Kovalev is well known for his formidable punching power.
Keith Thurman Jr. (born November 23, 1988) is an American professional boxer.
 He is currently a unified welterweight world champion, having held the WBA title since 2013 (promoted to Super champion in February 2017) and the WBC title since March 2017.
 As of July 2017 he is ranked as the world's best welterweight by the Transnational Boxing Rankings Board and "The Ring" magazine, and second by BoxRec.
 BoxRec also ranks him as the world's ninth best active boxer, pound for pound.
 Nicknamed "One Time," Thurman is known for his formidable knockout power and being one of the hardest punchers in the welterweight division.

Question: Who is most respected for giving the man ranked as the sixth best active boxer one of the toughest fights of his career?
Answer: Héctor Manzanilla Rangel