Pacheco was studying biology in Seville when he began working in comics, Pacheco's first published superhero comic was an eight-page story titled
American Soldier with writer and translator Antonio Moreno, and published as a back-up in
Marvel Héroes #41 (May 1991). Pacheco later teamed up with writer
Rafael Marín to create the characters Iberia Inc. and Tríada Vértice, two groups of Spanish superheroes, that starred in two miniseries published by Planeta-DeAgostini Comics under the imprint called "Línea Laberinto", with plots by Pacheco and Marín, script by Marín and art by
Rafa Fonteri (in
Iberia Inc.) and
Jesus Merino (in
Tríada Vértice). After that Pacheco's next stateside work came in 1995's
X-Universe two-part limited series (a part of the "
Age of Apocalypse" storyline), published by Marvel. Pacheco was joined by writer
Terry Kavanagh and was again inked by Cam Smith. In late 1995 and early 1996, Pacheco and Smith collaborated with writer
Warren Ellis on a
Starjammers limited series. This series was successful enough that the creative team was reunited on Marvel's
Excalibur ongoing series for a brief run in 1996. Shortly after this Pacheco became penciller on Marvel's
Fantastic Four for two issues (#415–416), where he worked with writer
Tom DeFalco as the title wrapped up in preparation for the "
Heroes Reborn" storyline. By that point Pacheco's art had become a fan favorite, with his work regularly getting coverage in magazines such as
Wizard. In early 1997 Marvel acknowledged this by assigning Pacheco to one of its flagship titles,
X-Men, with #62 (March 1997). On that title he worked with writers
Scott Lobdell and
Joe Kelly and inker
Art Thibert and produced the "
Operation: Zero Tolerance" storyline. He left the series at #75 in May 1998. and
Roger Stern and for the first time in the U.S. inker Jesus Merino, who from that point on became Pacheco's regular inker. Pacheco's next assignment was in 2000, a four-issue
Inhumans limited series, co-written with Rafael Marín with pencils by
José Ladrönn and
Jorge Lucas. Pacheco wrote, again with co-writer Rafael Marín, a return to the
Fantastic Four, with vol. 3 #35. This time he took on the co-writing chores (initially with Rafael Marín, later joined by
Jeph Loeb) as well as pencilling duties. Pacheco's pencilling contributions were shorter than expected, with his last art contribution coming in #50, and him leaving the series entirely by #54. for Best Limited Series. Pacheco returned to DC Comics to pencil the "Absolute Power" storyline in
Superman/Batman #14–18 (Jan.–April 2005), where he was again joined by writer Jeph Loeb. The two told a tale in which, due to the time-traveling machinations of the
Legion of Super-Villains,
Batman and
Superman took over the world and a group of
Freedom Fighters has to rise up against them. Later that year at DC, Pacheco shared alternate monthly pencilling duties with
Ethan Van Sciver on the new
Green Lantern series written by Geoff Johns. From 2006 to 2007, Pacheco worked with Kurt Busiek on DC comics'
Superman, illustrating issues #654–658, 662–664, and 667. Due to the difficulty of drawing twelve issues a year, the final chapter of their "Camelot Falls" story arc appeared in
Superman Annual #13 (January 2008). In February 2009,
Comic Shop News announced that Pacheco signed an exclusive contract with Marvel. Pacheco's 2009 work included
Ultimate Comics: Avengers. Pacheco was one of the artists on the
Age of Ultron limited series in 2013 and collaborated with writer
Rick Remender on the
Captain America series later that year. In 2022, Pacheco and Busiek reunited on a sequel,
Arrowsmith: Behind Enemy Lines, which garnered critical acclaim. In September 2022, Pacheco announced his retirement, and tweeted his final comics work, the cover to
Damage Control vol. 4 #2, which featured the characters
Ant-Man and
Wasp. ==Awards and accolades==