After World War II,  what came next was countries hiring agents to spy on one another in hopes of discovering and getting information about plans, tactics, weapons, and whatever intelligence reports they could get. Whether to get ahead of the other nations that posed a threat or just for the peace of mind that they won’t be surprised by a nuke one day, espionage agents became their countries’ secret weapons.

Double agents became a thing, too. Those spies pretended to work against the nation they were really loyal to, so they could get the juiciest of information, although some just betrayed their country. Here are the six who did:

Aldrich Ames

Aldrich Hazen Ames was one of the most infamous CIA traitors in the country. Nevertheless, he began his journey in the CIA. He had no plans of joining the organization, but after getting an outstanding GS-7 rating and high performance during his tests, he was accepted into the Career Trainee Program. He was assigned to various projects, but it was in his 1976 stint in New York that he started interacting with Soviet assets. During this mission, he received praises from the organization and even got promoted to one of the highest-ranking officers in his pay grade.

As he became increasingly involved in Russian intelligence in 1985, Ames was one of the officers assigned to assess Soviet embassy officials. CIA was looking to find potential intelligence assets at the time when the Russian offered him $50,000 for information.

Ames reportedly believed he only gave them “essentially valueless” information that would help him get closer to them, but he tried to play the double-agent game. He was enticed by the Russians, and it was easy money for him. Even when he was assigned to Washington, DC, in 1989, he continued what would now be known as “KGB drops.” Worse, he even let his wife (also part of the CIA) in his stint.

Ames thought he would evade being tracked by “outing” the Russians paying him to the US government. Then, in May 1993, the FBI opened a 10-month investigation where they found surmountable evidence of espionage and treason.

On Apr. 28, 1994, Ames and his wife pleaded guilty.

Donny Walker (John Anthony Walker)

John “Donny” A. Walker Jr. was a former Navy officer who created a spy ring, stealing military documents and selling them to the Soviets. He is still known as one of the most damaging spies in American History.

Walker was a Navy communications specialist during the Cold War. He started as a radioman in 1955 and worked his way up the ranks. He was a happy guy known as “Smiling Jack.” Eventually, he became a chief warrant officer in the Navy, handling sensitive information like locations of nuclear-armed submarines.

In 1967, he began extracting documents and passing them to the Soviets. During his early days, he worked alone and had no intentions of expanding his “spy ring.” The first leaked information he sent was a key for the Russians to read encrypted messages.

Then in 1980, Walker’s family got involved. His older brother’s radio business was failing, and since he was part of the recruitment, he advised his brother (Arthur) to pitch as a contractor. Unfortunately, this gave Arthur access to classified information, and the two began to tango.

John (Donny) also let his son, Michael, in to do some document shredding.

The trio was confident because nobody seemed to catch up to their schemes. But, in 1985, everything turned to ashes. A Soviet agent named Valery Martynov spoke to the FBI and betrayed John. Interestingly, Martynov was a contact for Ames, too.

The trio was found guilty, and in 2014, John “Donny” walker died at the age of 77.

Jonathan Pollard

Just like “Donny” Walker, Jonathan Jay Pollard was part of the Navy. But instead of communications, he was a civilian intelligence analyst and had been dreaming of becoming a spy since he was in college.

While studying at Stanford University, he would openly boast his peers that he had connections with Israeli intelligence and that his father was a CIA agent. Both of these were false. Still, he finished college with a degree in international relations. He tried applying to the CIA in 1977 but was rejected because of his drug use. The CIA also heard stories of his “tales” from previous classmates and deemed it problematic.

But, Walker didn’t stop there. In 1979, he was finally in the military, not the CIA but the Navy. IN 1984, he was able to move up the ladder and get assigned to US Navy’s Anti-Terrorist Alert Center. This was when he gained access to sensitive government files that connected him to the Israeli embassy. Just three months after he started in his new role, Israeli acquaintances claimed he sent them multiple classified documents without them asking.

He continued the scheme until he was captured on Nov. 18, 1985, as he walked out of his office with more than 60 classified documents in his briefcase.

Pollard pleaded guilty to espionage and was sentenced to prison for life. However, in 2020, he was allowed to return to his country, Israel.

The Rosenbergs

The two married in 1939 and resided in New York City. Julius and Ethel were communists who passed down top military secrets to the Soviets. They provided top-secret information about new radar and aircraft technologies, including sonar, jet propulsion engines, and the most controversial and valuable information: nuclear weapon designs, which only the United States had at that time.

The FBI arrested Ethel’s brother, David Greenglass, for espionage on June 15, 1950. He confessed that he was recruited by his sister’s husband, saying that Julius had passed the information and linked him to a KGB agent. As a result, the couple was arrested on suspicions of espionage. For decades, their sons and many other defenders argued and fought that the two were innocent and nothing but victims of Cold War paranoia. However, this proved untrue. Julius’ role as a courier and recruiter for the Soviets was revealed once the Soviet Union crumbled, complete with the decoded Soviet cables. Ethel also helped by doing clerical work like typing the documents that Julius passed to the KGB and recruiting his brother into espionage.

The two, convicted of espionage, were sent to the Sing Sing Correctional Facility in Ossining, New York, in 1951. They were executed via electric chair, the first American civilians to ever be executed for such.

Klaus Fuchs

Klaus Emil Julius Fuchs was a German theoretical physicist who decided to flee to the United Kingdom after Hilter’s rise to power. There, he received his doctorate in physics and was eventually invited to be a part of Britain’s atomic bomb development program, despite knowing he was leaning into communism. As a result, he was sent to the US to be part of the Manhattan Project. While at the Los Alamos National Laboratory, he was assigned to do many significant theoretical calculations about the first nuclear weapons and early models of the hydrogen bombs.

In the 1950s, US agents arrested him after discovering that he had been spilling nuclear secrets to the Soviets. At that time, Russia already had its atomic bomb technology. He confessed, saying he had complete confidence in Russian policy. However, he claimed not to know his American contact, who was the Rosenberg couple and some other co-conspirators. He served nine years in the UK prison before being set free and moving to East Germany, where he continued working as a physicist.

 Adolf Tolkachev

In multiple instances, Tolkachev attempted to connect with the CIA by dropping notes into the cars of US diplomats, asking to speak with an American official. He was a Soviet electronics engineer who claimed to have a grudge with the Soviets for having his wife’s mother murdered and his father imprisoned. Initially, he was ignored, but his persistence made the CIA trust him and allowed him to work with them.

So from 1979 to 1985, he would take a photo of classified information using a CIA-provided camera before handing them discretely to the CIA agents. Because of him, the US learned that their missiles and bomber planes could go undetected under the Soviet’s radar. Tolkachev also provided detailed information about projects like R-23, R-24, and S-300 missile systems used on the MiG-29.

He was paid more than $1 million for his service until it ended in 1985 when he was believed to be tipped by former CIA agent Edward Lee Howard or possibly by Aldrich Ames and executed.