Police tape blocks off a Waffle House restaurant on April 22 in Nashville, where at least four people were killed after a gunman opened fire. (Mark Humphrey/AP)

The nation’s favorite all-night comfort-food institution has humble origins. Two friends with an idea — a 24-hour restaurant.

Joe Rogers Sr. and Tom Forkner threw open the doors on the first Waffle House outside Atlanta in 1955. As the franchise spread, the chain’s iconic yellow signage popped up across the South. The concept has since pulled in a devoted fan base, from cash-strapped college students to early-bird seniors and everyone in between.

By the company’s count, Waffle Houses have served up 2.5 billion eggs, 1.8 billion hash brown orders and 877 million waffles.

“It is indeed marvelous — an irony-free zone where everything is beautiful and nothing hurts; where everybody regardless of race, creed, color or degree of inebriation is welcomed,” Anthony Bourdain waxed poetic on a 2015 episode of his CNN show “Parts Unknown.”

But that ubiquity comes with an underbelly, the most extreme example of which came Sunday. Police say Travis Reinking, naked except for a jacket, walked into a Waffle House outside Nashville about 3:30 a.m. He was carrying an AR-15 and allegedly opened fire on the restaurant, killing four before fleeing, they said.

On the same day, police forcefully removed a woman from a Waffle House in Saraland, Ala. Video of the arrest has prompted outrage.

It’s not the fault of Waffle House. But like Walmart stores, Waffle House locations are public places where people mix, often after hours, sometimes in altered states. The chemistry can contribute to confrontations and violent incidents, including homegrown terrorism plots and shootings.

“Because of round-the-clock service, crazy stuff famously goes down at the Waffle House,” Andrew Knowlton wrote in a 2015 Bon Appétit article. “There are robberies, cars crashed into facades, and, more commonly, obnoxious boozed-up customers simply behaving badly late, late at night. (Let’s be honest: If the French Laundry were open 24 hours a day, sketchy things would happen there too.)”

Although Waffle House is often in the news, the company has pushed back against any stigma.

“You can’t escape stereotypes,” a company spokesperson told the New York Times in 2011. “It’s not that more of these stories happen at Waffle Houses. It’s just getting more attention when it happens at a Waffle House.”

The brand’s wide appeal has some effect on the drama unfolding inside.

According to the company, more than 1,500 Waffle Houses are in operation, including restaurants owned by the parent corporation and by franchisers. The Southern-fried feel of the 1950s diner culture — rare in the 21st century — attracts various demographics to the locations. The restaurants’ hours — open all day, every day, even holidays — also keep a steady stream of customers coming through the door, especially late at night, when other options are closed.

Waffle Houses are so reliable, the federal government even uses the chain as a “barometer for disaster recovery,” Eater has reported. The Federal Emergency Management Agency uses a “Waffle House Index” to weigh the damage of violent storms — if the weather was fierce enough to close down a stalwart like Waffle House, the government knows it was bad.

“It’s classic diner culture with a Southern accent,” Jim Auchmutey, a food writer for the Atlanta Journal-Constitution, told the Christian Science Monitor in 1999. “They’ve taken something simple and folksy at heart and replicated it like crazy.”

“There’s something intangibly egalitarian about the place,” a Waffle House fan told the same paper. “Anyone fits in at a Waffle House; everyone feels welcome.”

The chain’s consistency is the key to that appeal, and that goes beyond the items on a menu. “Income inequality may be a hot-button issue in the United States, but the Waffle House doesn’t discriminate,” GQ wrote last year in an ode to the chain. “Everyone sits at the same Formica table; everyone eats the same crispy hash browns; everyone pays the same prices. In this nation that is scattered, smothered and covered, Waffle House is where America is its truest, an oasis where we can all unite free of prejudice and preconceived notions.”

But if a Waffle House is an egalitarian melting pot, it has also been a collision point.

For example, in 2007, Kid Rock was accused of hitting a patron after a disagreement inside an Atlanta Waffle House, according to Business Insider. The rock star was sentenced to one year of probation and forced to pay a fine.

In 2011, four elderly men were arrested in Georgia after allegedly plotting to attack government buildings. The men hatched their plan over breakfasts at a local Waffle House.

A year later, a gunfight in the parking lot of a Memphis Waffle House left one man dead.

In October 2015, an irate customer reportedly shattered the front door of a Waffle House in Atlanta after learning the price of sausage biscuits had risen to $1.50 from $1.00.

A month later, a Mississippi Waffle House waitress was reportedly shot by a customer after she told him to put out his cigarette.

The next year, a Waffle House employee at another Atlanta-area location was arrested for allegedly spiking her co-worker’s drink with methamphetamine.

In January 2016, a customer became enraged, stripped naked and punched a woman in the nose in an “excited delirium state.”

Last January, two Waffle House employees in Arkansas were caught washing their hair in the restaurant’s kitchen.

Many Waffle Houses are located directly off a highway, creating a further tempting target for robbers, police and security experts say.

Strange happenings at Waffle House restaurants continue. On Sunday afternoon, as investigators and corporate staff members continued to work the crime scene at the location outside of Nashville, a car pulled into the parking lot. According to 10 News, when a Waffle House manager walked up to the vehicle, he saw that the woman behind the wheel had just given birth.

The new mother had gotten into a minor accident while driving herself to a hospital. Waffle House staff members called emergency responders to the scene, and the mother and newborn were taken to a hospital.

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