The Most Excellent (Spanish: Excelentísimo Señor (male) or Excelentísima Señora (female), literally "Most Excellent Sir/Madam") is an honorific prefix that is traditionally applied to certain people in Spain and certain Spanish-speaking countries. Following Spanish tradition, it is an ex officio style (the holder has it as long as they remain in office, in the most important positions of state) and is used in written documents and very formal occasions.
The prefix is similar (but not equal) to that of "His/Her Excellency", but in the 19th century "The Most Excellent" began to replace the former.
The proper use of the prefix Excellency was re-introduced in Francoist Spain by Generalísimo Francisco Franco himself, who was formally styled as Su Excelencia el Jefe del Estado ("His Excellency The Head of State"), while his ministers and senior government officials continued using the prefix "The Most Excellent".
The following State and Government officials receive the style "The Most Excellent":
The style "His Excellency", which has a higher connotation than "The Most Excellent", is instead reserved for the children of an Infante or Infanta, who have the have the rank (but not the title) of Grandees.
During Francoist Spain, General Francisco Franco was the de facto Dictator of Spain and properly adopted the style His Excellency, since he was both Chief of State and Government, without being a "royal".
Following the tradition from Spain, Hispanic countries adopted the styles "His Excellency" and "The Most Excellent" although they are informally used most of the time without following rules of style.
Properly used, the style "His Excellency" (or simply "Excellency") is reserved for Chiefs of State and/or Government in Republics, i.e. the President and Vice-President of the Republic. Also, though informally, this style applies for the "President of Congress" (or equivalent) and the "President of the Supreme Courts" (or equivalent). Former Presidents and Vice-Presidents of Republics usually retain the style "His/Her Excellency" after finishing their terms, as an honorific.
The style "The Most Excellent" (Excelentísimo Señor/a) applies to high-ranking officials of Republican countries that are not Chiefs of State or Government, i.e. a Minister, a Governor, an elected official.
Ambassadors of Foreign Countries also receive the style "The Most Excellent", although informally they are addressed as "Excellency".
In other countries, "His Excellency" and "The Most Excellent" are rarely used.
In the United States, albeit rarely, the President of the Nation is styled "Excellency". The more British-style "The Honourable" is preferred for Senators, Representatives and other elected officials.