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