Social Security numbers serve as sort of a national ID for American citizens, but it wasn’t always that way. When economist Edwin Witte helped develop the Social Security Act of 1935, the numbers were solely a way to keep track of the new retirement payment system.

Witte and his colleagues “knew they needed an ID number, not just a name,” says John Witte—who, in addition to being a professor emeritus of political science at the University of Wisconsin-Madison, is Edwin’s grandson. That way even if people had the same name or birthday as others, their payments could be tracked with an individual number.

Even so, the assignment of Social Security numbers, or SSNs, was controversial. The U.S. government had never distributed individual numbers like this before, and some “were very frightened of giving the government the ability to have a number to track people,” Witte says.

Despite some Republicans’ contention that it was government overreach, the Social Security Act passed in the Democrat-led Congress in August 1935; and “the first SSN was issued sometime in mid-November 1936,” says Dorothy J. Clark, a Social Security spokesperson.

At first, Social Security was only meant for certain workers. Domestic workers, agricultural workers, and small business employees were ineligible, and federal employees weren’t part of the program because they already had government pensions for retirement. The program mainly targeted large, private companies, requiring them to offer Social Security to their employees.

Over the next few years, the government created millions of them. While the Social Security Board was still setting up offices around the country, the Post Office played a huge administrative role by distributing and collecting applications and generating Social Security numbers.

“We don’t think about this much today, but it was an enormous administrative undertaking,” Witte says. “Creating a social security system, writing the act, and getting the money was only part of it. The biggest, difficult thing was implementing that program.”

Subsequent legislation over the next few decades expanded the eligible Social Security pool until it included all American citizens—including children. When the U.S. first passed the act, only adults could sign up for Social Security. But by 1989, when the Enumeration at Birth program made it easier for parents to apply for babies’ SSNs as soon as they’re born, that had all changed. Today, Witte notes that you have to provide your children’s SSN in order to claim them as a dependent on your taxes.

In fact, the number’s ubiquity is part of why Witte says the U.S. probably won’t stop using SSNs as a national form of ID. There are so many things modern Americans need their SSN to apply for—driver’s licenses, homes, college admissions and more—that the government would have to come up with a different kind of ID that could be substituted in its place.

“It would be an enormous task to replace it with something else,” Witte says, of a White House proposal to do stop using SSNs as a form of national ID in the wake of the massive Equifax data breach that exposed 145 million people’s personal information between May and July 2017. And even if it did happen, he muses, “What would that do?” If hackers could get access to SSNs, why couldn’t they gain access to another form of ID?

Likely, the system that necessitates we all memorize our own nine-digit number will continue for a long time.

READ MORE: Where Social Security Came From