Ubaldo Matildo Fillol ([uˈβaldo maˈtildo fiˈʎol]; born 21 July 1950), nicknamed el Pato (lit. 'the Duck'), is an Argentine former professional footballer who played as a goalkeeper. He took part in the 1974, 1978 (where he won the championship with his team and was voted Best Goalkeeper) and 1982 World Cups representing the Argentina national team. He also played in the South American qualifiers for the 1986 World Cup, but he was finally not chosen for the final team that played (and won) in Mexico. He is considered one of the best Argentine goalkeepers ever.

Born in San Miguel del Monte, Fillol took his first steps as goalkeeper in an amateur club of the city, where he spent four years. Former River Plate player and manager Renato Cesarini would be his mentor after seeing him play at the regional league. In 1965 Fillol arrived to Quilmes A.C. to play at club's youth divisions. At the age of 18, Fillol debuted in the Argentine top division playing for Quilmes vs. Huracán on 1 May 1969. He soon drew public attraction due to his agility and quick reflexes that allowed him to make acrobatic saves.

In the 1970 Metropolitano championship Fillol stopped the first penalty in his career to Gimnasia y Esgrima LP forward Delio Onnis. That same year Quilmes would be relegated to Primera B, where Fillol played 23 matches with the club. In 1972 Fillol was signed by Racing Club de Avellaneda, debuting in the 1972 Metropolitano tournament. In that championship, Fillol set a record of six penalties saved, the highest in Argentine football for a single season.

In 1973 Fillol was transferred to River Plate, where he would play for most of his career. At River Plate, Fillol won seven titles, including the 1975 Metropolitano tournament, the club's first title in 18 years. In 1977 Fillol was awarded the footballer of the Year of Argentina, being the first goalkeeper ever to receive the distinction.

He was called up for the Argentina national team, where he was part of the roster at the 1974 World Cup (the other goalkeepers were Daniel Carnevali and Miguel Ángel Santoro). Fillol's most notable performance with Argentina was in 1978, when Argentina won its first World Cup and Fillol was chosen as the best goalkeeper of the competition.

In 1983, after a conflict with River Plate management (during which he considered retiring) Fillol was transferred to Argentinos Juniors by request of former River coach Ángel Labruna, who was managing Argentinos at the time. Fillol played 17 matches there. In November that year, he moved to Brazil to play for Flamengo. There, he won the Taça Guanabara with the club in 1984.

Fillol's debut in European football was in 1985 when he was transferred to Atlético Madrid at the age of 35. With Fillol as goalkeeper, the club won the 1985 Supercopa de España. In 1986 Fillol returned to Racing, where he won the first edition of the Supercopa Sudamericana in 1988, which was also the club's first international title since the 1967 Intercontinental Cup

The best goalkeeper I've ever seen was Ubaldo Fillol"