Horn was born in Athens in 1921, the son of playwright Pantelis Horn (himself descended from an Austrian father and Greek mother), and Euterpi, a Pontic Greek.

During his career, he co-operated many times with the Greek National Theater and made personal stage troops with actors such as Mary Aroni, Alekos Alexandrakis and Ellie Lambeti.

From an early stage he developed a reputation as "the best actor of his generation," performing many classics such as "Diary of a Madman" by Nikolai Gogol, Richard III by William Shakespeare, Dom Juan by Molière, and Enrico IV by Luigi Pirandello to critical acclaim.

His screen work was less important to him; he disliked cinema,[1] only starring in ten films.

He later married shipping heiress Anna Goulandri, and became the first director of the Greek State Radio and Television after the restoration of democracy.