Marcelo Vieira da Silva Júnior (born 12 May 1988), known as Marcelo, is a Brazilian professional footballer who plays as a left-back for Campeonato Brasileiro Série A club Fluminense. Known for his offensive capabilities, trickery, and technical qualities, Marcelo is often regarded as one of the greatest left-backs of all time. He spent most of his career with Spanish club Real Madrid and is the club's most decorated player, with 25 trophies won.

Starting his professional career with Fluminense in 2005, Marcelo won a Campeonato Carioca title on his debut season and was named in the 2006 Brasileirão Team of the Season. In January 2007, he joined Real Madrid for an $8 million fee. In Madrid, he went on to be a mainstay and has won five UEFA Champions League titles and six La Liga titles, among other honours. In 2021, Marcelo became the captain of Real Madrid from the start of the 2021–22 season, making him the first foreign captain since 1904. After leaving Madrid in 2022, he had a five-month spell at Olympiacos, followed by a return to Fluminense in 2023, where he managed to win the Copa Libertadores. He has been named in the FIFPro World XI six times, the UEFA Team of the Year three times, and La Liga's Team of the Season in 2016. He was also named to France Football's "Team of the Decade (2010–2019)".

Having debuted for Brazil in 2006, Marcelo was called up for the 2008 Olympic squad, where he won a bronze medal. Four years later, he was part of Brazil's 2012 Olympic team as one of the three over-age players, winning a silver medal. Marcelo was selected to play in the 2013 FIFA Confederations Cup and started all five matches, as Brazil won 3–0 against Spain in the final. He was part of Brazil's squad at two FIFA World Cups (2014 and 2018) and he was named in both tournament's Dream Teams.