The Confederate flag. Burning crosses. The Nazi swastika. Pepe the Frog.

One of those may not sound like the others, but according to the Anti-Defamation League, they’re all hate symbols.

On Tuesday, the Anti-Defamation League announced that Pepe the Frog, a cartoon that became one of the Internet’s most popular memes, has been added to its “Hate Symbol Database.”

Becoming a bona fide hate symbol is a far cry from the green guy’s origin as a character in Matt Furie’s comic book series “Boy’s Club,” which ran in the mid-2000s. In the Amazon product description for the comic, Pepe and his three other anthropomorphic animal friends are “”drinkin’, stinkin’ and never thinkin.'”

Furie described the comic to The Washington Post’s Abby Ohlheiser as “pointless, early 20-something college humor.”

He told the Daily Dot that Pepe was conceived from the joy he feels when he would see a frog. He said:

Seeing a frog always takes my breath away and brings a genuine smile to my face. That is what I want every reader to experience each time they think about the “Boy’s Club” comic — a thrill of overwhelming beauty and joy!

And, for a while, that’s exactly what the frog was, even when it became a meme — a source of joy. Users on message boards like 4chan and Reddit posted images of the frog to represent happiness.

As Ohlheiser wrote, “4chan distilled Pepe down to a single moment from that cartoon, where Pepe finally answers for his unusual, ‘pants all the way to the ground’ approach to relieving himself. Pepe smiles and explains, ‘Feels good man.’ That’s the earliest Pepe meme, basically a reaction meme of the frog saying that phrase.”

Eventually, the image was modified to represent an array of emotions, from “feeling good” to feeling far less than that.

Some celebrities, like Katy Perry, even posted images of the frog to connect with their audiences.

Recently, though, images of the frog with tattoos depicting racist symbols like swastikas and the number 88 — each 8 represents “H” for its place in the alphabet, the meaning being “Heil Hitler” — began appearing. In modified images, the frog often boasted an orange coiffure a la Donald Trump. (Trump even shared one such post.)

He had been appropriated by the alt-right.

Here's what you need to know about the alt-right movement. (Jenny Starrs/The Washington Post)

“Once again, racists and haters have taken a popular Internet meme and twisted it for their own purposes of spreading bigotry and harassing users,” Jonathan A. Greenblatt, ADL chief executive, said in a news release. “These anti-Semites have no shame. They are abusing the image of a cartoon character, one that might at first seem appealing, to harass and spread hatred on social media.”

While the cartoon frog finds himself among the decidedly dark company of the swastika and the Confederate battle flag, he also finds himself alongside seemingly innocuous symbols on the Hate Symbols Database like “100%” and “737.” To the lay observer, these appear to be potential references to how much of a bottle of juice is made from actual fruit or what the make of a particular airplane is, but they’re references to white supremacist ideas — “100%” means “100% white” and “737” refers to a California-based white supremacists gang.

Similarly, the “Coors” logo, according to the ADL, doesn’t always refer to a light beer from the Rockies but to “Comrades of our Racial Struggle.” Taylor Swift has become an alt-right “Aryan goddess” icon, and the “Betsy Ross” flag recently set off controversy when students flew it at a football game because some white supremacist groups had appropriated it as their own symbol.

These are all seemingly innocuous symbols and references whose alternative meanings aren’t immediately apparent to someone who isn’t aware of their (appropriated) hateful connotations — and that might be exactly the point.

“It shouldn’t surprise us that bigots are early adopters of technology,” Greenblatt told the New York Times. “Their noxious views are difficult to circulate openly.” And via social media, “they can post something to Twitter or Facebook and achieve exponential reach under a cloak of anonymity.”

And racist people have been sneakily using technology not just to spread their ideology but to connect with each other for years. It was a way of being invisible in the open.

Take “echo,” or the act of putting someone’s name in multiple parentheses [e.g., (((Travis))) Andrews]. At one point, it was considered an “Internet hug,” but anti-Semitic members of the alt-right co-opted it as a means of identifying Jewish people on the Internet in hopes that other anti-Semites might spam that user with hateful tweets.

It was an effective means of communications too, as New York Times deputy Washington editor Jonathan Weisman learned after a Twitter user named @CyberTrump placed his name in an “echo.”

“The anti-Semitic hate, much of it from self-identified Donald J. Trump supporters, hasn’t stopped since,” Weisman wrote in a column about his harassment.

The echo was eventually added to the Hate Symbols Database.

As Ryan Milner, a communications professor at the College of Charleston who studies online groups, told the New York Times, racist messages are now spread “not through crosses burned on front lawns, but through little bits of conversation shared on Twitter,” which “then spread to classrooms and bars and living rooms.”

Pepe the Frog is the latest casualty of this behavior.