More than a decade ago, when Russia pushed Pavel Durov to shut down the pages of opposition politicians on a Facebook-like site he had created, the tech entrepreneur responded online by posting a cheeky picture of a hoodie-wearing dog with its tongue out.

“Official response to the intelligence services to the request to block groups,” he wrote unapologetically.

Thirteen years later, Mr. Durov’s anti-establishment streak appears to have gotten him into a fresh round of trouble with the authorities. On Saturday, he was arrested in France as part of an investigation into criminal activity on Telegram, the online communications tool he founded in 2013, which had grown into a global platform defined by its hands-off approach to policing how users behaved.

On Monday, President Emmanuel Macron of France referred to Mr. Durov’s arrest and said that the country was “deeply committed to freedom of expression” but that “in a state governed by the rule of law, freedoms are upheld within a legal framework, both on social media and in real life.”

Mr. Durov’s arrest has caused a firestorm, turning him into a folk hero among those concerned about free speech and government censorship, especially as scrutiny of online content has increased globally. Elon Musk, the owner of X, and Edward Snowden, the American intelligence contractor who fled to Russia after disclosing classified information, were among those who raced to Mr. Durov’s defense. The hashtag #FreePavel spread on X as debate raged over the murky intersection between tech and freedom of speech.

Telegram said in a statement on Sunday that it abides by European Union laws. “It is absurd to claim that a platform or its owner are responsible for abuse of that platform,” the company said.