In the main text of your written work, use a suffix that is an essential part of the name—like Jr. or a roman numeral—when you cite a person’s name in full. Do not place a comma before numbered suffixes:
John D. Rockefeller IV
Place a comma before Jr. and Sr.:
Dale Earnhardt, Jr.
In a sentence, add a comma after Jr. or Sr. if words follow; the suffix is parenthetical:
Sammy Davis, Jr., was a member of the rat pack.
But see the MLA Handbook, section 2.1.2, on inverting such names in the list of works cited.
Published 23 August 2016