Do I use a comma before Jr. and Sr.? What about names followed by roman numerals?

Note: This post relates to content in the eighth edition of the MLA Handbook. For up-to-date guidance, see the ninth edition of the MLA Handbook.

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.