The Most Excellent (Spanish: Excelentísimo Señor (male) or Excelentísima Señora (female), literally "Most Excellent Lord/Lady") 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 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 prefix "The Most Illustrious" (Ilustrísimo/a Señor/a) is the lower version, and is mostly used for non-Grandee titled nobles in Spain and some other officeholders.