Namesakes
Bishops of Rome and the Popes:
1 antipope, 1 pope
Constantine 708-715 
Constantine II 767-768
Bulgarian Kings and Tsars:
3 tsars
Tsar Petar III (a.k.a. Constantine) 1072
Tsar Konstantin I (a.k.a. Constantine) 1257-1277
Tsar Konstantin II (a.k.a. Constantine) 1397-1422
Greek Prime Ministers:
2 prime ministers
Constantine Kanaris 1844; 1848-1849; 1864; 1864-1865; 1877
Konstantinos Karamanlis (a.k.a. Constantine) 1955-1958; 1958-1961; 1961-1963; 1974-1980
Hall-of-Famers:
1 football
(football) Johnny Unitas (middle name Constantine) 1979
Most Valuable Players:
1 winner
Johnny Unitas (middle name Constantine) 1964; 1967 football
Notable Athletes:
1 football
(football) Johnny Unitas (middle name Constantine) 1933-2002
Notable Filmmakers:
1 director/screenwriter
Alexander Payne (a.k.a. Constantine) 1961-
Notable Writers:
1 poet
Konstantinos Petrou Kavafis (a.k.a. Constantine) 1863-1933
Olympic Medalists:
1 bronze, 1 gold
(gold) Konstantinos II (a.k.a. Constantine) 1960 sailing - dragon
(bronze) Constantine Louloudis 2012 rowing
Other Leaders:
1 president
President Konstantinos Karamanlis (a.k.a. Constantine) 1980-1985; 1990-1995 Greece
Other Royalty:
1 king
Konstantinos II (a.k.a. Constantine) 1964-1973 Greece
Roman and Byzantine Emperors:
11 emperors
Emperor Flavius Valerius Aurelius Constantinus (a.k.a. Constantine) 306-337
Emperor Flavius Claudius Constantinus (a.k.a. Constantine) 337-340
Emperor Heraclius Novus Constantinus (a.k.a. Constantine) 641
Emperor Constantinus (a.k.a. Constantine) 668-685
Emperor Constantinus (a.k.a. Constantine) 741-775
Emperor Constantinus (a.k.a. Constantine) 780-797
Emperor Constantinus Porphyrogenitus (a.k.a. Constantine) 913-959
Emperor Constantinus (a.k.a. Constantine) 1025-1028
Emperor Constantinus Monomachus (a.k.a. Constantine) 1042-1055
Emperor Constantinus Ducas (a.k.a. Constantine) 1059-1067
Emperor Constantinus Palaeologus Dragases (a.k.a. Constantine) 1449-1453
Saints:
2 saints
Saint Constantine the Great c. 272-337
Saint Constantine ?-874
Scottish Kings and Queens:
4 kings
King Causantín mac Fergus (a.k.a. Constantine) 789-820
King Causantín I (a.k.a. Constantine) 862-877
King Causantín II (a.k.a. Constantine) 900-943
King Causantín III (a.k.a. Constantine) 995-997