Was Mata Hari actually a spy?
The evidence that she did any meaningful espionage is remarkably weak, and modern historians largely regard her as a woman executed for reasons that had more to do with French morale in 1917 than with anything she passed to Germany.
Who she was. Margaretha Zelle, born in the Netherlands in 1876, married an officer, lived in the Dutch East Indies, and after a miserable marriage reinvented herself in Paris as an exotic dancer with a fabricated Javanese background. She became genuinely famous, and moved among wealthy and well-connected men across Europe — including, as a neutral national able to cross borders, officers on both sides of the war.
What she was accused of. Passing information to German intelligence as agent H21, causing the deaths of thousands of soldiers.
Why historians doubt it:
The intercepted messages that condemned her were sent by the German attaché in Madrid in a code the Germans knew the French had broken. Historians have long argued this looks like a deliberate attempt to have a useless or compromised agent eliminated by the French themselves.
No evidence of consequential information was ever produced. The claimed death toll appears in the prosecution's rhetoric rather than in any documentary chain.
She had approached French intelligence herself and agreed to work for them — a fact that complicates the simple picture considerably.
The trial was closed and the defence severely constrained, with limited access to evidence.
The context matters. 1917 was France's worst year — the Nivelle offensive had failed, mutinies had spread through the army, and a visible traitor was politically useful. She fitted the role: foreign, sexually unconventional, and unsympathetic to a conservative court.
She was executed by firing squad in October 1917. The theatrical details — blowing a kiss, refusing a blindfold — are of uncertain reliability and have grown in retelling.
Her name became a byword for the seductive female spy, a stock figure her actual life mostly fails to support.