Final answer:
Henry Clay was the author of the Missouri Compromise and Compromise of 1850, and he is often referred to as the "Great Compromiser".
Step-by-step explanation:
The author of the Missouri Compromise and Compromise of 1850, who is often referred to as the "Great Compromiser", is Henry Clay. Henry Clay was a prominent American politician and lawyer who played a crucial role in the early 19th century in enacting these significant pieces of legislation. He led the efforts to find a compromise between the North and the South on the issue of slavery.