Yanni (later John) Alexis Mardas (Greek: Αλέξης Μάρδας; born May 5, 1942, Athens, Greece), better known as Magic Alex, the name given him by The Beatles when he knew the group between 1965 and 1969, is a self-styled electronics wizard and one-time head of The Beatles' Apple Electronics.

Mardas arrived in England in 1965, exhibiting his Kinetic Light Sculptures at the Indica Gallery. Mardas impressed John Lennon with the Nothing Box; a small plastic box with randomly blinking lights, and said that he could build a 72-track tape machine, so was given the job of designing the new Apple Studio in Savile Row. He was involved in the hasty departure of Lennon and George Harrison from the Maharishi Mahesh Yogi's ashram in India, and Lennon's divorce of his first wife, Cynthia Lennon.

In the 1970s, the anti-terrorism industry offered bullet-proof vehicles, bugging devices and security hardware, and Mardas set up various companies offering these products to royalty and VIPs. King Hussein of Jordan bought a fleet of cars that Mardas had customised, but the cars proved to be more life-threatening than ordinary cars, as bullets easily pierced the supposed armour-plating, and the glass splintered. In 1987, Mardas was a managing director of Alcom Ltd, which specialised in electronic communications and security. He now lives in Greece.