Guillermo Castro Martín (born 11 November 1973) is a Spanish retired footballer who played as a defender.
He helped the former promote to Segunda División in 1996, making his debut in the competition on 31 August of that year by playing 45 minutes in a 0–0 away draw against UD Almería.
[2] At the end of 1999–2000, Castro also won promotion with Universidad – a first ever – appearing in 35 games the following season in an immediate relegation.
[3] He split the 2001–02 campaign between Elche CF (second division)[4] and AD Ceuta (Segunda División B).
Castro retired in 2004 at the age of 30, after a second spell with both Universidad and Las Palmas and following relegation from the second tier with the latter.