Rex was born in Munich as Ludwig Alexander Hirtreiter.

He sold over 25 million records and the biggest hit that Rex had was "Fiesta Mexicana (Hossa)" in 1972 and after his death it became a hit again when the New York Rangers played it whenever their winger Marcel Hossa scored.

In 1962 he did a cover version of Pat Boone's "Speedy Gonzales". He married his cousin Marion Hirtreiter in 1974, probably as a career move as he continued having gay affairs and then a permanent partner.

He appeared in at least thirty feature films such as "Hit Parade '60" and "The Magic Apartment" (1963). When his style of music "Schlager" went out of fashion in the 1980s he was reduced to performing in beer halls and shopping malls.

He died of heart failure three days after jumping from his third floor apartment in Munich and was buried next to his long term partner Fred Miekley who had died in 1988.