Roberto Fabián Ayala ([roˈβeɾto faˈβjan aˈʝala]; born 14 April 1973), nicknamed El Ratón ("The Mouse"), is an Argentine former footballer who played as a centre back for the Argentina national football team, as well as Valencia and Real Zaragoza in Spain, Milan and Napoli in Italy, and Ferro Carril, River Plate and Racing Club in his native Argentina.

Regarded as one of the best central defenders of his generation, he stood out for his leadership and ability in the air throughout his career in spite of his small stature as a centre back.

[7] He soon established himself as a first choice central defender for Los Che and started alongside compatriot Mauricio Pellegrino in the 2001 UEFA Champions League final, where Valencia lost 5–4 to Bayern Munich after a penalty shootout.

[7] During the 2004–05 season, injuries kept Ayala from much of the La Liga campaign as well as the UEFA Super Cup victory over Porto.

During his time with Valencia, he was widely regarded as one of the finest central defenders in the world and is considered to be one of the club's all-time legends.

He played for Argentina in the 1998 FIFA World Cup and was a non-playing squad member in the 2002 competition due to a last-minute injury moments before their first match against Nigeria.

In the quarter-final against Germany, he scored a header that gave Argentina the 1–0 lead, although his side lost the penalty shootout after a 1–1 draw, with Ayala's spot kick being saved by Jens Lehmann.

[15] On 17 July 2007, two days after playing in the 2007 Copa América Final, which ended in a 3–0 defeat to Brazil, and during which he scored an own goal, Ayala announced his retirement from international football.

[21] On 10 January 2019, Ayala joined the technical staff of the Argentina national football team as a field assistant of manager Lionel Scaloni.

[2] Regarded as one of the best and most accomplished defenders of all time, Ayala was mainly known for his ability in the air and tenacious tackling, and also stood out for his leadership and consistency throughout his career.