A number of degrees with a similar title were conferred in the British Isles in the 18th century. They were, Excellent Masons, Super Excellent Mason, Excellent Master, and an obscure degree in Scotland called Most Excellent Master. These degrees differed in content but were each considered to be prerequisite to the Royal Arch Degree in whatever jurisdiction they were worked.
Many Masonic historian credit Thomas Smith Webb with fabricating the Most Excellent Master Degree as it is worked in modern America. He may have written the American ritual, however, the main theme is that of the Most Excellent Master Degree known in Scotland in the 18th century.
The earliest references to woeking this degree in America were in Middletown, Connecticut in 1783, and in Newburyport Chapter in Massachusetts on January 1, 1797. The degree could well have been conferred here prior to 1783.
This is the only Masonic degree that deals with the completion of the temple. The craftsman is confronted with many valulable lessons for his future development.
Excerpted from: A History and Handbook, The York Rite of Freemasonry, by Frederic G. Speidel