Final answer:
Legendary composer/lyricist Stephen Sondheim wrote the classics Sweeney Todd, Sunday in the Park with George, Company, and Into the Woods, significantly impacting musical theater with his sophisticated lyrics and innovative structures.
Step-by-step explanation:
The composer/lyricist who wrote classics such as Sweeney Todd, Sunday in the Park with George, Company, and Into the Woods is the legendary Stephen Sondheim. Sondheim is renowned for his contributions to musical theater and is justifiably considered one of the most important figures in the genre. His works are characterized by their complex musical structure, sophisticated lyrics, and the ability to address darker or more serious themes within the context of a musical.
Stephen Sondheim's influence in musical theater is profound, particularly noted in the transition period of the 1970s when traditional narrative structures were giving way to more experimental forms such as the concept musical. His work in Company revolutionized the musical theater landscape by introducing this new form, which focuses more on themes and ideas rather than a straightforward plot. The era also saw the rise of socially responsible theater, moving away from the romantic escapades and instead, addressing more serious and thought-provoking issues, something Sondheim's work exemplified.