The DNI is the identity document used in Spain. Each citizen currently has an eight-figure number and a letter in his. This identification method was born as a result of a decree on March 2, 1944.

The DNI number 1 was given to Francisco Franco in 1951. Number 2 went to his wife, Carmen Polo, and number 3 was assigned to their daughter, Carmen Franco. The numbers between 4 and 9 were left free, while those between 10 and 99 are reserved for the Spanish royal family.

In this way, the DNI with the number 10 belongs to King Emeritus Juan Carlos I and 11 to his wife Sofía. Number 12 belongs to the Infanta Elena and number 14 to the Infanta Cristina. The 13 was left vacant by the superstition around this number. King Felipe VI, who was a prince at that time, was later assigned the number 15. His daughters, the Infantas Leonor and Sofía, have the numbers 16 and 17, respectively.

The first DNI design was created by Aquilino Rieusset Planchón, who won a public contest and received a prize of 30,000 pesetas. It was green and included data on the profession and position of the citizen. It also had a box that classified it according to its economic status in different categories.

Zaragoza was the first capital of a Spanish province where the DNI was issued, but it took years for this document to be extended to the entire population. The first people forced to formalize it were prisoners and those who remained on probation. They were followed by men who, due to their profession, frequently changed their addresses.

In third place were men who lived in cities with more than 100,000 inhabitants and in fourth place were those who lived in towns with a population between 25,000 and 100,000 inhabitants. Women traveling for work were next on this priority list.

According to the criteria of The Trust Project