Sergio Bismarck Villar (born 5 January 1944) is a Uruguayan former footballer who played as a left back.

In 1968 Villar joined San Lorenzo and in his first year with the club they won the Metropolitano championship, and became the first team in the professional era of Argentine football to complete a season without losing a game.

In 1972 Villar was part of the San Lorenzo team that won both of the Argentine league titles, this time they completed the Nacional championship without losing a single game.

Villar is one of only five players to have won four league championships with San Lorenzo, the others being Roberto Telch, Victorio Cocco, Carlos Veglio and Agustín Irusta.

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