Theo Albrecht, the secretive retail tycoon who built the no-frills Aldi supermarket empire with his elder brother Karl, has died aged 88.

Albrecht, who was Germany's second-richest man after his brother, with a fortune worth nearly €17 billion ($24.7 billion), had kept a low profile after being kidnapped at gunpoint in 1971. He has been buried in his native Essen.

Theo Albrecht ... he and his brother followed their mother into grocery shops.

Mystery surrounded his birth date, reported to be either March 13 or March 28, 1922. His mother started a small grocery shop in Essen after their father, a miner, developed the lung condition emphysema. Theo and his brother followed in her footsteps. They went into business together after returning from the war - Theo in Rommel's Afrika Korps and Karl on the Russian front. They began opening tiny shops that sold butter, milk, bread and other basics. By 1953, they had 31 shops around Essen with combined sales of $US3 million. By 1960, they had 300 stores across Germany with sales of $US45 million.

In the same year, the brothers split the retailer in two - purportedly after arguing over whether to sell cigarettes - and agreed not to make incursions into each other's territory. Karl took charge of the stores in southern Germany (Aldi-Sud) and Theo managed the northern division (Aldi-Nord), with his two sons.