Saint Olga of Kyiv
This is one unsaintly saint. Olga’s husband, Igor I, Prince of Kyiv, was murdered by a group living in Kyiv known as the Drevlyans, because they didn’t want to pay him what they thought was an excessive tribute. Olga and Igor’s son was still an infant, so she became the land’s ruler, and the Drevlyans soon sent ambassadors to negotiate a marriage between her and their choice for king. When they arrived, it’s said she had a moat dug and buried them alive.
Not even nearly done, Olga reportedly sent word back that she needed better suitors, but when the Drevlyans sent more men, she locked them in a bathhouse and set fire to it. She then went to visit the Drevlyans personally, and they held a great feast in her honor, and then once they were drunk her men slaughtered them all.
As the Drevlyans recognized her power, they asked for mercy and offered goods in exchange. Olga then requested three sparrows and pigeons from each household in the city. Sounds harmless, right? Well, she had all the birds fitted with pieces of sulfur in small pieces of cloth, then released them back into the city and set it ablaze.