Q. In the name Joaquín “el Chapo” Guzmán, should the definite article be capitalized? My reading of CMOS 8.5 and 8.35 seems to suggest that “el” should be lowercased in running text and capitalized only when it appears at the beginning of a sentence. Thank you for your time and guidance!
A. In both Spanish and English, spell the definite article with an initial cap when such a nickname is placed in quotation marks and offered as an alternative form of the name rather than as part of the name or as a purely descriptive epithet (as in the two examples featuring Ivan, who isn’t usually referred to by his epithet alone):
Joaquín “El Chapo” Guzmán
Bruce “The Boss” Springsteen
but
Ivan the Terrible or Ivan IV, “the Terrible”
In subsequent mentions (without quotation marks), an initial cap helps to differentiate Spanish-language names from the surrounding English-language text but is usually unnecessary for names in English. In other words, you can refer to El Chapo (capital E) but the Boss (lowercase t), though fans of the rock icon might prefer that you call him The Boss.