"[1] Mullen was born in New Haven, Connecticut, U.S. on August 30, 1843,[2] and attended the public schools there.

[6] When Father Michael McGivney first conceived of creating the Order, he proposed the name the Sons of Columbus.

[7] Mullen instead suggested using Knights instead of Sons to better exemplify the ritualistic nature of the nascent organization.

[10] On the train ride to Meriden, Mullen assigned Daniel Colwell the responsibility of devising the installation ceremony.

[11] As Supreme Knight, Mullen supported the expansion of the Order outside of Connecticut, a contentious issue at the time.

[12] Colwell and Mullen joined McGivney in presenting the ceremonials of the Order to Bishop Lawrence McMahon of the Diocese of Hartford to ensure they were acceptable for a Catholic organization.

[21] Mullen enlisted in the 9th Connecticut Infantry Regiment on September 11, 1861 and served as a sergeant in the Civil War.

[2] He became a successful businessman[2] following his apprenticeship painting ornamental signs he became a commercial traveler.