ex-, former, then

Hyphenate ex- as a prefix when it means former:

            ex-governor Patricia Edmonds

            ex-farmer

However, former is preferable, especially when space permits:

            former president Ronald Reagan

            the former first lady

Do not use former when reference is made to something done while a person held a position; then may be used:

            then chief justice Warren E. Burger 

No hyphen in compounds unless ambiguous:

            then photographer Chris Johns

See late, latter, former.