Con O'Brien may refer to:

• Con O'Brien (American football) (1898–1993), American football player
• Con O'Brien (politician) (1866–1938), Australian politician

• Ioannis Roufos
• Ioannis Sioutis
• Ioannis Skylitzes
• Ioannis Sofianopoulos
• Ioannis Theodorakopoulos
• Ioannis Theotokis
• Ioannis Tsimiskis
• Ioannis Varvakis
• Ioannis Vilaras
• Ioann Konstantinovich of Russia
• Ioann Krestyankin
• Ioann of Kronstadt
• Ioannou & Paraskevaides
• Ioan Ovidiu Sabău
• Ioan Pascu
• Ioan Paşcu
• Ioan Pașcu
• Ioan P. Couliano
• Ioan Potcoava
• Ioan Potcoavă
• Ioan Puscas
• Ioan Pușcaș
• Ioan Rilski
• Ioan Roata
• Ioan Roată