Namesakes
Eurovision Song Contest Winners:
1 winner
Duncan Laurence 2019 Netherlands 
Fictional Characters from Television:
1 character
Duncan Kane 2004 Veronica Mars
Hall-of-Famers:
1 ice hockey
(ice hockey) Mickey MacKay (a.k.a. Duncan) 1952
Nobel Prize Winners:
1 physics
(physics) Duncan Haldane 2016
Notable Actors and Entertainers:
3 actors
Jeffrey Jones (a.k.a. Duncan) 1946-
Duncan Regehr 1952-
Robert Duncan McNeill 1964-
Notable Athletes:
1 cricket, 1 rugby
(cricket) Hamish Rutherford (a.k.a. Duncan) 1989-
(rugby) Duncan Weir 1991-
Notable Musicians:
1 singer
Duncan Laurence 1994-
Notable Scientists and Inventors:
1 physicist
Duncan Haldane 1951-
Olympic Medalists:
3 gold, 2 silver, 1 gold/bronze, 1 gold/silver
(silver) Duncan Gillis 1912 hammer throw
(gold) Dunc Munro 1924 ice hockey
(gold) Duncan McNaughton 1932 high jump
(silver) Duncan M. White 1948 400 m hurdles
(gold/bronze) Duncan Goodhew 1980 swimming - 100 m breaststroke; swimming - 4x100 m medley relay
(gold/silver) Duncan Armstrong 1988 swimming - 200 m freestyle; swimming - 400 m freestyle
(gold) Duncan Keith 2010; 2014 ice hockey
Other Royalty:
1 prince
Leopold, Duke of Albany (a.k.a. Duncan) 1853-1884 United Kingdom
Scottish Kings and Queens:
2 kings
King Donnchad I the Gracious (a.k.a. Duncan) 1034-1040
King Donnchad II (a.k.a. Duncan) 1094
Shakespearian Characters:
1 character
Duncan Macbeth