“I don’t know if he’s guilty [of corruption] or not,” Headache Stencil says. “But I wanted to show we’re alarmed.”

Alarmed, that is, by what anti-junta activists see as endemic corruption under the military regime. The army seized power in 2014 from a democratically elected government ostensibly with the aim of eradicating corruption and restoring social harmony after months of fractious street protests.

Recently, Headache Stencil produced another piece, this one on a concrete support for an elevated road. It shows a Thai soldier in combat fatigues taking aim with a plastic water gun of the kind revellers use during the Thai New Year known as Songkran.

“It’s the fourth year we’ve had Songkran under military rule,” Headache Stencil observes. “That’s what I wanted to say with it.”

The authorities clamp down on dissent, so presumably Headache Stencil does his graffiti furtively at night? No. He works in broad daylight. “Why would I do it at night?” he says. “It’s dark, bro. I couldn’t see a thing.”

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Dressed in overalls, he dons a face mask and shows up at preselected locations with his stencils and paints. “I look like a workman,” he says. “No one realises I’m going to do graffiti. Passers-by think I’m there to repaint a wall or repair something.”

Headache Stencil dresses in a casual hip-hop style, is covered in tattoos and speaks fluent English peppered with American slang.

“I’ve always been a bad boy, bro,” Headache Stencil says. “Look at the tattoos of opium poppies on my arms, man,” he adds. They complement a portrait of Diego Maradona that takes up his left shoulder.

The Thai street artist had the retired Argentine footballer’s face inked into his skin in homage as much to Maradona’s legendary dribbling skills as to his reputation as a devil-may-care party animal.

A former creative marketing professional who worked in the entertainment business, Headache Stencil also used to party hard. He does less of that now. He also tries to guard his anonymity. “It’s dangerous for me, bro,” he notes.

Shortly after his tongue-in-cheek take on the deputy prime minister’s penchant for luxury watches went viral on social media, municipal officials whitewashed the image and a dozen police officers showed up at the graffiti artist’s condominium. Headache Stencil gave them the slip just in time.

From hiding, he reached out to his tens of thousands of followers on Facebook. Saying he feared for his safety, he stressed he was no criminal. “All I did was express my views through art,” he wrote. “I didn’t kill anyone. So what’s the point of this harassment?”

Several young pro-democracy activists staged a protest in his support at a Bangkok landmark and were promptly detained for violating the law against political gatherings without permission. “It’s not about graffiti. It’s about free speech,” says one activist who studies at a university in the Thai capital.

In the end, the authorities backed off. Headache Stencil remains jittery, though. He speaks freely to a reporter but asks that details like his family background be left unmentioned, even if they’re known to the police.

But he won’t make apologies for his art. “I’ve called myself Headache for a reason, bro,” he says. “I want to give some [powerful] people a headache.”

He’s not alone in that.

In recent months street art has turned into a potent form of social commentary in Thailand. While most local graffiti has long existed in the usual no-man’s-land between vandalism and artistic self-expression, much of it now carries overtly political undertones.

The recent killing of a black panther in February galvanised the artists. A story broke that a hunting party headed by Premchai Karnasuta, a wealthy construction magnate, had been detained by wildlife rangers inside a World Heritage wildlife sanctuary in central Thailand. Premchai was discovered with the carcasses of several freshly killed animals, including a black leopard.

The mogul was taken briefly into custody where he was photographed receiving deferential treatment from a senior police officer. To Thais, long used to a culture where the rich and powerful can get away with murder, it seemed the case would become yet another in which the authorities failed to prosecute a rich man standing accused of a crime.

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Then, a few days later, a stencilled mural of a roaring black panther appeared on a wall in Bangkok. Next to it was a vector icon for the “mute” function on smartphones. The message was clear: there would soon be silence on the matter of the big cat. The graffiti bore the hallmarks of Headache Stencil.

Before long, street artists far and wide began calling for justice for the dead animal by spray-painting stylised black panthers in public spaces. In one elaborate mural, an artist in the northern city of Chiang Mai pictured the businessman blindfolded with a military ribbon rack and flanked by two leopard skulls.

“Many people don’t want to speak out because they’re scared,” says Piyasak Khieosaard, the 33-year-old artist behind the image. “But somebody has to do it.”

A mild-mannered man with a ponytail and a wispy goatee, Piyasak once sold noodles on the street. He now spends his time spray-painting imaginative animal-themed images onto walls to critique the maltreatment of animals.

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“We have to keep reminding people of environmental and social issues so they don’t fade from view,” he says. “I try to make my paintings eye-catching, but it’s their message that matters.”

The construction billionaire, who is facing several poaching-related charges, has denied any wrongdoing or killing the leopard.

“I didn’t do it,” he told Thai media. It was business as usual, he added, for his conglomerate that has worked on several lucrative government projects over the years. “I called all bureaus and ministries, and everyone felt sorry for me,” he said.

But Mardi, a world-weary, doll-faced cartoon character in a rabbit costume, doesn’t buy his denials. He’s the brainchild of Patcharapol Tangruen, a 37-year-old artist who goes by the moniker Alex Face, who has decorated numerous walls, facades and other surfaces around Bangkok and other cities with his trademark creation.

Recently his character appeared on a concrete fence, wearing a black panther costume with a pointy Pinocchio nose. “Liars [are] gonna lie,” the artist says.

“The killing of the leopard isn’t just about poaching. It’s also a matter of justice,” says Petch Manopawitr, a prominent Thai conservationist. “Graffiti artists have helped keep the focus on this case. They’ve definitely made an impact.”

In the process, Headache Stencil, Piyasak, Patcharapol and other street artists have become celebrities in their own right. “Everyone in my area knows me, bro,” Headache Stencil says. “The security guards, the papaya salad sellers, the street cleaners.”

Not everyone is pleased with his new-found fame, though. “Many of my friends and relatives don’t get it,” he says. “They don’t want me to rock the boat.”

But he’ll carry on. “If people see my work and start noticing that things aren’t fair, I’ve achieved my aim,” he says.