Comrade X/Madame X was one of the great espionage agents of the Soviet Union. She was a master of disguise and stealth. She had some military training and used conventional weaponry. She also once used a special gas-firing weapon. She initially cross-dressed as a man, using a latex mask, a padded uniform and a vocal modification device.
The Soviet Union had been attempting for a while to steal the Pym Particles method of shrinking from Hank Pym (Ant-Man). Since other agents had already tried and failed, Comrade X was next assigned the mission. Contacting Pym as a woman, she posed as a former lover of Comrade X. She warned Pym of the Comrade plotting against him and sent him to board a freighter at Pier 89. Naturally it was a trap but Ant-Man managed both to defeat Comrade X and to reveal her as Madame X. Ant-Man had her arrested by the United States coast guard.
Later she allied with other old enemies of Hank Pym in a plot against Pym and the West Coast Avengers. She was defeated by MODAM, posing at the time as Maria Troyvana Pym - long lost wife of Hank.