Question: Kelly Robert Pavlik (born April 5, 1982) is an American former professional boxer who competed from 2000 to 2012, he made three successful title defenses before losing them to which Argentine former professional boxer, who competed from 1997 to 2014?
Context: Sven Ottke (born 3 June 1967) is a German former professional boxer who competed from 1997 to 2004.  He was a unified super-middleweight world champion, having held the IBF title from 1998 to 2004, and the WBA (Super) title from 2003 to 2004.  He made 21 successful title defences, and was the third European boxer to retire as an undefeated world champion, after Terry Marsh and Michael Loewe; Joe Calzaghe later became the fourth.  As an amateur, Ottke won a bronze medal in the middleweight division at the 1989 World Championships. Eduard Gutknecht (born 19 March 1982) is a German former professional boxer who competed from 2006 to 2016.  He won the European light-heavyweight title in 2011, making three successful defences before losing it to Jürgen Brähmer in 2013.  Gutknecht also challenged for the WBA light-heavyweight title, losing in a rematch against Brähmer in 2016. Sergio Gabriel Martínez (born February 21, 1975) is an Argentine former professional boxer who competed from 1997 to 2014.  He held the unified WBC, WBO, "Ring" magazine, and lineal middleweight titles between 2010 and 2014, making six successful defenses of the latter two titles.  Martínez's 50-month reign as lineal champion ranks as one of the longest in middleweight history.  He also fought at light middleweight, where he held the IBO title from 2003 to 2005, and the WBC interim title in 2008 (later elevated to full world champion status the following year). Iván Calderón Marrero (born January 7, 1975) is a Puerto Rican former professional boxer who competed from 2001 to 2012.  He is a two-weight world champion, having held the WBO mini flyweight title from 2003 to 2007 (making eleven successful defenses and being recognized as super champion by the organization), and the WBO, " Ring" magazine, and lineal light flyweight titles from 2007 to 2010 (making six successful defenses).  Additionally, his August 2010 bout against Giovani Segura was named fight of the year by " Ring" magazine.  As an amateur Calderón represented Puerto Rico in international competitions, including the 2000 Olympics. Walter Dario Matthysse (born August 29, 1978) is an Argentine former professional boxer who competed from 2002 to 2009, and challenged once for the IBF welterweight title in 2007.  He is the elder brother of professional boxer Lucas Matthysse. Brian 'The Lion' Rose (born 15 February 1985) is an English professional boxer.  He was the WBO Intercontinental and British Champion and is part of a select group that has retained the Lonsdale Belt having made three successful defences of the British title beating Prince Arron to initially win the title.  His retention of the belt came in his third defence against the former belt holder Sam Webb in a unanimous decision. Christopher Cornelius "Chris" Byrd (born August 15, 1970) is an American former professional boxer who competed from 1993 to 2009.  He is a two-time world heavyweight champion, having first won the WBO title in 2000 after an upset corner stoppage over then-undefeated Vitali Klitschko.  In his first title defense later that year, he lost to Vitali's brother Wladimir Klitschko.  In 2002, Byrd defeated Evander Holyfield to win the IBF heavyweight title for his second reign as world champion.  He made four successful defenses until losing his title again to Wladimir Klitschko in a 2006 rematch.  Byrd's cousin, Lamon Brewster, has a shared history with Wladimir Klitschko: Brewster defeated him in 2004, but lost in a 2007 rematch. Carlos Manuel Baldomir (born April 30, 1971) is an Argentine former professional boxer who competed from 1993 to 2014.  He held the WBC, "Ring" magazine, and lineal welterweight titles in 2006, and challenged once for the WBC super welterweight title in 2007. Hozumi Hasegawa (長谷川 穂積 , Hasegawa Hozumi , born 16 December 1980) is a Japanese former professional boxer who competed from 1999 to 2016.  He is the fourth Japanese boxer to win world titles in three weight classes, having held the WBC bantamweight title from 2005 to 2010; the WBC featherweight title from 2010 to 2011; and the WBC super bantamweight title in 2016.  Hasegawa received MVP awards from the Japan Boxing Commission in 2005, 2006, 2008, and 2009 for his title defenses, and is the first Japanese boxer to have defended a bantamweight world title more four times. Kelly Robert Pavlik (born April 5, 1982) is an American former professional boxer who competed from 2000 to 2012.  He won the unified WBC, WBO, "Ring" magazine and lineal middleweight titles by defeating Jermain Taylor in 2007, and made three successful defenses before losing them to Sergio Martínez in 2010.
Answer: Sergio Gabriel Martínez