Short answers, pulled from the story.
The People's Republic of Bulgaria existed from 1946 to 1990. The monarchy was abolished by plebiscite in 1946, and the state officially dissolved on the 12th of July 1991 when a new constitution removed all symbols of the former regime.
Vasil Kolarov served as prime minister until his death, after which Vulko Chervenkov assumed both titles. Chervenkov ruled from 1950 to 1955 before ceding party leadership to Todor Zhivkov in 1954 while remaining prime minister.
A campaign of forced assimilation began in the winter of 1984 where ethnic Turkish minorities were forbidden to speak their language and forced to adopt Bulgarian names. This policy caused significant economic damage due to the loss of approximately 300,000 agricultural workers following the 1989 expulsion of Turks from Bulgaria.
Bulgaria earned the nickname Silicon Valley of the Eastern Bloc by developing computers such as the Vitosha and Pravetz models. The state currently operates an IBM Blue Gene/P supercomputer, making it the only Balkan country with such infrastructure.
The seventh Grand National Assembly voted on the 15th of November 1990 to change the country name to Republic of Bulgaria and remove the Communist state emblem from the national flag. All symbols of the People's Republic of Bulgaria were officially dissolved on the 12th of July 1991 with the adoption of a new constitution.