Mr. Thanakorn was arrested at his home in a Bangkok suburb last week and had not been seen until his arraignment on Monday. Among other charges, he is accused of sharing on Facebook allegations of corruption in the military’s construction of a monument to previous kings.

The royal dog in question is Tongdaeng, or Copper, who is widely loved in Thailand.

King Bhumibol Adulyadej, 88, who is also beloved and is ailing in a Bangkok hospital, rescued the mongrel from an alley; in 2002 he wrote a best-selling book about her. The Thai news media use the polite honorific “khun” to describe the dog, a term that roughly translates to ma’am.

Image In 2002, the king wrote a book about his dog, Tongdaeng, who is widely known and loved in Thailand. Credit... Sukree Sukplang/Reuters

The book describes Tongdaeng as a “respectful dog, with proper manners.” The king appeared to intend it as an allegory about the importance of respect and etiquette in changing times.

Tongdaeng “is humble and knows protocol,” the book’s preface says. “She would always sit lower than the king.”

Despite the unusual nature of the charges against Mr. Thanakorn, there was relatively little discussion about the case on Monday on social media, perhaps because of fears that those who highlighted it might also face charges.