One of the best midfielders in Guatemala's history, Guillero "El Pando" Ramírez was a player with a hybrid role, a creative player and a goal threat in critic occasions, using blending technical finesse with leadership.

After playing for CSD Municipal since 1995, Ramírez signed with PAS Giannina of Grecia in 2001. After a year in the Grecian Super League, he returned home to the "Rojos". In January 2003, he reached the Mexican First Division by signing with Jaguares de Chiapas; the second half of the season, he played with Chiapas' reserve team in the Primera A. After that he came back to Municipal for the second half of 2004, winning the Interclubs Cup of 2004 with Municipal, their 1th international trophy since 2001.

In 2005, he went on loan to the Los Angeles Galaxy of the MLS, scoring the decisive goal in the Final against the New England Revolution, which gave the team of Los Ángeles their second title in history (Fun fact, his friend and team player Carlos "El Pescadito" Ruiz gave them their first cup in 2002).

At the end of the 2005 MLS season, he returned to Municipal and helped them win three league titles, where he won the Clausura 2006, Apertura 2006 and Clausura 2008, and being runner-up twice in the Apertura 2008 anc Clausura 2009.

In July 2009, he was transferred to Marathón of Honduras, where he won the National League of Honduras in the 2009-10 season.

After a year with the "Monstruo Verde", he returned to Municipal of Guatemala, where he was one of the protagonist of the most dramatic final in the history of the Liga Nacional, where he unfortunately failed a penalty in the runner-up of the Apertura 2010 against Comunicaciones. He scored his 130th goal on Sunday, August 29, 2010, surpassing the legend Carlos "Pepino" Toledo.

He made his debut for the Guatemala national team on June 16, 1997, in a match against Costa Rica in the 1997 UNCAF Cup; his first international goal was scored on January 23, 1998 against Trinidad and Tobago in the Guatemala's victory 3-1.

On August 6, 2008, El Pando was wearing the captain's armband when he scored Guatemala's second goal in a 3-0 victory over the Bolivian national team. He became the player with the most caps in the history of the Guatemala national team, with 87 caps in 2009, surpassing the previous record helded by Juan Carlos Plata. Today he has 106 caps, is the 2nd under Carlos "El Pescadito" Ruiz where he played 133 with the national team.