Alex Dimitriades (Greek: Αλέξανδρος Δημητριάδης, romanized: Aléxandros Dimitriádis; born 28 December 1973) is an Australian television, film and stage actor of Greek descent. He is perhaps best known for his roles as Nick Polides in the 1993 romantic comedy film The Heartbreak Kid and as Nick Poulos in the 1994 television teen drama spin-off Heartbreak High. He won critical acclaim for his role as Ari, a troubled second generation Greek Australian in Head On (1998), based on Christos Tsiolkas's 1995 novel, Loaded. He won the Film Critics Circle of Australia award for Best Actor for the role and was nominated for the AFI Award for Best Actor. He later starred in The Slap (2011) based on Tsiolkas's novel of the same name and won the AACTA Award for Best Lead Actor. He also starred in the titular role of the drama series, The Principal (2015) and won the Logie Award for Most Outstanding Actor. He has also had roles in a number of British-Australian co-productions such as The Cry (2018) and The Tourist (2022).

Dimitriades was born in Sydney, as Alexandros Dimitriades. He is the son of first generation Greek immigrants and the youngest of three siblings. He has a brother, George, and a sister, Melinda. He grew up in Earlwood, Sydney. His parents divorced when he was 12. His mother worked as a legal secretary, and she raised the children as a single mother.

Dimitriades first attracted national attention for his co-starring role as Nick Polides in the 1993 Australian romantic comedy film The Heartbreak Kid, for which he received positive reviews and acclaim.

In 1998, he played the protagonist Ari in the Ana Kokkinos film Head On, based on the book Loaded by Christos Tsiolkas. Dimitriades' performance in the role was critically acclaimed and earned him an AFI Award nomination. The film was controversial for its graphic violence, sex scenes and LGBT subject matter, but it earned mostly positive reviews. It screened at dozens of festivals around the world, including the Director's Fortnight at the 1998 Cannes Film Festival.

His other film roles include the Australian comedies Let's Get Skase (2001) and La Spagnola (2001), the Greek film To Gamilio Party (English title Bang Bang Wedding, 2008), Wog Boy 2: Kings of Mykonos (2010), and Summer Coda starring with Rachael Taylor. He had roles in the Hollywood films Ghost Ship (2002) and Deuce Bigalow: European Gigolo (2005).

In 2015, he co-starred in Ruben Guthrie with Patrick Brammall.

After making his acting debut in the film The Heartbreak Kid, he starred in a television spin-off Heartbreak High, in which he played Nick Poulos. He went on to play underworld figure, Warren Lanfranchi, in the 1995 drama television series Blue Murder. The following year, Dimitriades played estate agent Steve George in the television soap opera Neighbours. In 1997, he took a role in the police drama Wildside.

In 2002, he appeared in Young Lions. In years to follow, he had a small guest role in the Australian science fiction series Farscape. In 2008, Dimitriades starred in the drama series Underbelly.