How did Modest Mussorgsky adapt Boris Godunov into an opera?

Modest Mussorgsky adapted Aleksandr Pushkin’s drama into the opera Boris Godunov by creating his own libretto, which largely set Pushkin’s lines as they were originally written.12

The adaptation process involved two major versions:
* First Version (1869): Mussorgsky completed the initial draft, but it was rejected by the imperial theatres' advisory committee for lacking a prima donna role.1
* Second Version (1872): To address these concerns, the composer revised the work, adding the roles of Marina and Rangoni, as well as several new episodes.1

Musically, Mussorgsky infused the work with dramatic intensity by fusing arioso and recitative and employing unorthodox tonality and harmony. He also incorporated a Macbeth-inspired hallucination scene and drew upon Shakespearean stylistic elements, such as balancing epic tragedy with popular comedy and the fate of the realm. The final version premiered successfully in 1874.12