Namesakes
Bishops of Rome and the Popes:
2 popes
Marcellus I 308-309 
Marcellus II 1555
Fictional Characters from Plays and Musicals:
1 character
Marcellus Washburn 1957 The Music Man
Saints:
5 saints
Saint Marcellus the Centurion ?-298
Saint Marcellus ?-304
Saint Marcellus I ?-309
Saint Marcellus of Apamaea ?-389
Saint Marcellus ?-510
Shakespearian Characters:
1 character
Marcellus Hamlet