Olga of Kiev, also known as Saint Elena, was a viking queen who live from ~890-925, and ruled in territories of modern day Ukraine, Russia, and Belarus. Olga's husband, Igor, was murdered after returning to the tribe of the Drevlians, which had a shaky relation with Igors empire, and murdered Igor when he requested further payment (the payment in question was tribute to Igors predecessors, to which the Drevlians had stopped paying until confronted). Upon Igors death, Olga assumed power of the throne as her son, Sviatoslav, was too young at the time. Just as Olga began to grieve for her husband's death, the Drevlians sent 20 negotiators to try and convince Olga to marry their prince (the reason for this was an attempt to keep Olga from retaliating against the Drevlians). Olga responded calmly and requested they return tomorrow so that she may gather her people to hear the news. The next day, the 20 negotiations returned in their boats, and repeated what they had requested to Olga. Her people then picked up the boats with the men still in them and peraided them through town until they arrived at the court to which they were unceremoniously thrown into a hole, their soon to be grave, with Olga mocking them as they were buried alive. Afterwards, Olga sent a request to the Drevlians to send men to help safely bring her to their kingdom, to which the Drevlians abliged. Upon arrival, Olga offered the men a bath, and when they entered the bath house, Olga herself set the door on fire and let the men burn to death. Olga sent another request for the Drevlians to prepare mass amounts of mead so that when she arrives, they may have a large feast and so she may grieve over her husband's grave. The Drevlians, again, obliged and prepared the mead as requested. Olga did go to the Drevlians and feast and grieve, however had herself and her men not indulge as much as the other attendants. When the attendants had drunk themselves to sleep, Olga and her men killed what is estimated to be 5,000 men in a single night, all of which were the party attendants. Olga would leave and return with an army at her side and a year long conflict would insue. With little results from either side, Olga would request they stop fighting and the Drevlians agreed, though stated they were still scared she still wanted revenge. Olga promised to leave them be under the condition that each house hold bring three pigeons and sparrows to her. When done, each bird had a sack of sulfer tied to their legs, with it set on fire, and released back into the city where almost every house was burned down. This would finally satiate Olga's blood lust. In ~950, Olga would travel to Constantinople and would convert to Christianity, and would then attempt to peacefully introduce her kingdom to it.
Just to be clear they killed her husband because he was blackmailing them in what amounts to a Mafia protection racket and the people who she murdered were largely the general populace. It's funny we revile ordinary evil men who would rob and murder a family but cheer for a mass murderer .