A friend's post over at the Super Champion Film Zone reminded me that a lot of well-known directors have made trilogies of one kind or another. Some are traditional trilogies, a film and two sequels, but in others there's a less direct link among the films - a location, a character, a theme. Some are planned, some are only appreciated by critics after the fact. Either way, they appear below if a single director was responsible for all three of the films.
To appear on the list, all three films must share the same director, all three films need to have actually been produced, and all three films need to be on letterboxd. I found several examples on a wikipedia…
A friend's post over at the Super Champion Film Zone reminded me that a lot of well-known directors have made trilogies of one kind or another. Some are traditional trilogies, a film and two sequels, but in others there's a less direct link among the films - a location, a character, a theme. Some are planned, some are only appreciated by critics after the fact. Either way, they appear below if a single director was responsible for all three of the films.
To appear on the list, all three films must share the same director, all three films need to have actually been produced, and all three films need to be on letterboxd. I found several examples on a wikipedia page ("list of film series with three entries"), but the list there is enormous, and includes hundreds of trilogies that don't fit the criteria here.
The directors and trilogies are listed below.
1-3: Abbas Kiarostami's Koker Trilogy
4-6: Tengiz Abuladze's Georgian Historical Trilogy
7-9: Roy Andersson's Living Trilogy
10-12: Ingmar Bergman's Trilogy of Faith
13-15: Satyajit Ray's Apu Trilogy
16-18: Krzysztof Kieslowski's Three Colours Trilogy
19-21: Aki Kaurismaki's Proletariat Trilogy
22-24: Francis Ford Coppola's Godfather Trilogy
25-27: Mrinal Sen's Calcutta Trilogy
28-30: John Ford's Cavalry Trilogy
31-33: Howard Hawks' Western Trilogy
34-36: Wim Wenders' Road Movie Trilogy
37-39: Masaki Kobayashi's Human Condition Trilogy
40-42: Joao Cesar Monteiro's Joao de Deus Trilogy
43-45: Richard Linklater's Before Trilogy
46-48: Michelangelo Antonioni's Modern Alienation Trilogy
49-51: Wong Kar-Wai's Love Trilogy
52-54: Tsai Ming-liang's Taipei Trilogy
55-57: Lars von Trier's Europa Trilogy
58-60: Lars von Trier's Golden Heart Trilogy
61-63: Takashi Miike's Black Triad Trilogy
64-66: Takashi Miike's Dead or Alive Trilogy
67-69: Peter Greenaway's Tulse Luper Trilogy
70-72: Pier Paolo Pasolini's Trilogy of Life
73-75: Fritz Lang's Dr Mabuse Trilogy
76-78: Jean-Pierre Melville's Delon Trilogy
79-81: Luchino Visconti's German Trilogy
82-84: Hou Hsiao-hsien's Taiwan Trilogy
85-87: Edward Yang's Urban Trilogy
88-90: Park Chan-wook's Vengeance Trilogy
91-93: Yasujiro Ozu's Noriko Trilogy
94-96: Jean Cocteau's Orphic Trilogy
97-99: Carlos Saura's Dance Trilogy
100-102: Sergio Leone's Dollars Trilogy
103-105: Michael Haneke's Glaciation Trilogy
106-108: Dario Argento's Three Mothers Trilogy
109-111: Terry Gilliam's Trilogy of Imagination
112-114: Terry Gilliam's Trilogy of Americana
+ Terry Gilliam's Orwellian Trilogy (Brazil, Twelve Monkeys, The Zero Theorem) overlaps with the two trilogies included in the list
115-117: John Carpenter's Apocalypse Trilogy
118-120: Sam Raimi's Evil Dead Trilogy
121-123: Christopher Nolan's Dark Knight Trilogy
124-126: Oliver Stone's Vietnam War Trilogy
127-129: Peter Jackson's Lord of the Rings Trilogy
130-132: Gus van Sant's Death Trilogy
133-135: Alejandro Gonzalez Inarritu's Death Trilogy
136-138: Nicolas Winding Refn's Pusher Trilogy
139-141: Steven Soderbergh's Ocean's Trilogy
142-144: Robert Rodriguez's Mexico Trilogy
145-147: Bruce McDonald's Road Trilogy
148-150: Pang Brothers' Eye Trilogy
151-153: Hiroshi Inagaki's Samurai Trilogy
154-156: Godfrey Reggio's Qatsi Trilogy
157-159: Raoul Walsh's What Price Glory Trilogy
160-162: Lindsay Anderson's Mick Travis Trilogy
163-165: Cedric Klapisch's Auberge Espagnole Trilogy
166-168: Patrice Leconte's Les Bronzés Trilogy
169-171: Im Kwon Taek's General's Son Trilogy
172-174: Renato Castellani's Italian Neorealism Trilogy
175-177: Marta Meszaros' Diaries Trilogy
178-180: Mani Ratnam's Political Trilogy
181-183: Aktan Abdykalykov's Coming of Age Trilogy
184-186: Amos Gitai's Wadi Trilogy
187-189: Amos Gitai's Exile Trilogy
190-192: Amos Gitai's City Trilogy
193-195: Amos Gitai's Israel History Trilogy
196-198: Amos Gitai's Frontier Trilogy
199-201: Theo Angelopoulos' Trilogy of History
202-204: Theo Angelopoulos' Trilogy of Silence
205-207: Theo Angelopoulos' Trilogy of Borders
208-210: John Ford's Will Rogers Trilogy
211-213: Zeki Demirkubuz's Dark Tales Trilogy
214-216: Semih Kaplanoglu's Yusuf Trilogy
217-219: Andrzej Wajda's War Trilogy
220-222: Roberto Rossellini's War Trilogy
223-225: Roman Polanski's Apartment Trilogy
226-228: Tsai Ming-liang's Urban Alienation Trilogy
229-231: King Hu's Inn Trilogy
232-234: Lucio Fulci's Gates of Hell Trilogy
235-237: Dario Argento's Animal Trilogy
238-240: James Benning's California Trilogy
241-243: David Lynch's Los Angeles Trilogy
244-246: Gregg Araki's Teenage Apocalypse Trilogy
247-249: Léos Carax's Alex Trilogy
250-252: Bob Rafelson's Dysfunctional Family Trilogy
253-255: Ken Loach's West of Scotland Trilogy
256-258: Lucas Belvaux's Trilogie
259-261: Steven Spielberg's Running Man Trilogy
262-264: Penelope Spheeris' Decline of Western Civilzation Trilogy
265-267: James Gray's New York Crime Trilogy
268-270: Lars von Trier's Depression Trilogy
271-273: Coen Brothers' Idiot Trilogy
274-276: John Frankenheimer's Paranoia Trilogy
277-279: Hou Hsiao-hsien's Coming of Age Trilogy
280-282: Pedro Costa's Fontainhas Trilogy
283-285: Alfred Hitchcock's Apartment Trilogy
286-288: Lisandro Alonso's Lonely Man Trilogy
289-291: Ismael Rodriguez's Trilogy of Bittersweet Poverty
292-294: Felipe Cazals' Violence Trilogy
295-297: Rainer Werner Fassbinder's BRD (Bundesrepublik Deutschland) Trilogy
298-300: Seijun Suzuki's Taisho Trilogy
301-303: Miguel Gomes' Arabian Nights Trilogy
304-306: Ritwik Ghatak's Partition Trilogy
307-309: Yoshishige Yoshida's Trilogy of Japanese Radicalism
310-312: Alexander Dovzhenko's Ukraine Trilogy
313-315: Vsevolod Pudovkin's Revolutionary Trilogy
316-318: Deepa Mehta's Elements Trilogy
319-321: Ludmil Staikov's Khan Asparukh Trilogy
322-324: Jerzy Hoffman's Henryk Sienkiewicz Trilogy
325-327: Kim Ki-Young's Housemaid Trilogy
328-330: Jean-Claude Brisseau's Female Sexuality Trilogy
331-333: Terence Davies' The Terence Davies Trilogy
334-336: Bill Douglas' The Bill Douglas Trilogy
337-339: Rudolf Thome's Time Travel Trilogy
340-342: Dominik Graf's Melodramas Trilogy
343-345: Thomas Arslan's Berlin Trilogy
346-348: Romuald Karmakar's Club Land Trilogy
349-351: Klaus Lemke's Leidenschaften Trilogy
352-354: Chang Cheh's One-Armed Swordsman Trilogy
355-357: Edgar Wright's Cornetto Trilogy
358-360: The Wachowskis' The Matrix Trilogy
361-363: Robert Zemeckis' Back to the Future Trilogy
364-366: Peter Jackson's The Hobbit Trilogy
367-369: Andrew Lau and Alan Mak's Infernal Affairs Trilogy
370-372: Wilson Yip's Ip Man Trilogy
373-375: Sion Sono's Hate Trilogy
376-378: Zhang Yimou's Wuxia Trilogy
379-381: Edgar Reitz's Heimat Trilogy
382-384: Baz Luhrmann's Red Curtain Trilogy
385-387: Brett Ratner's Rush Hour Trilogy
388-390: Akio Jissoji's Buddhist Trilogy
391-393: Liu Chia-Liang's 36th Chamber Trilogy
394-396: Shigehiro Ozawa's Street Fighter Trilogy
397-399: Kazuhiko Yamaguchi's Karate Trilogy
400-402: Ann Hui's Vietnam Trilogy
403-405: Patricio Guzman's The Battle of Chile Trilogy
406-408: Whit Stillman's Whit Stillman Trilogy
409-411: Guillermo del Toro's Trilogia
412-414: Nacer Khemir's Desert Trilogy
415-417: Luca Guadagnino's Trilogy of Desire
418-420: Ulrich Seidl's Paradise Trilogy
421-423: Juan Antonio Bayona's Mother-Child Trilogy
424-426: Sergei Parajanov's Caucasian Trilogy
427-429: Philippe Garrel's Trilogy of Love
430-432: Barbet Schroeder's Trilogy of Evil
433-435: Roberto Rossellini's Fascist Trilogy
436-438: Satyajit Ray's Calcutta Trilogy
439-441: Sam Raimi's Spider-Man Trilogy
442-444: Jean-Pierre Melville's Resistance Trilogy
445-447: Jose Mojica Marins' Coffin Joe Trilogy
448-450: Bigas Luna's Iberian Trilogy
451-453: Herschell Gordon Lewis' Blood Trilogy
454-456: Sergio Leone's Once Upon a Time Trilogy
457-459: Takeshi Kitano's Outrage Trilogy
460-462: Takeshi Kitano's Surrealist Autobiographical Trilogy
463-465: Richard Fleischer's Capital Punishment Trilogy
466-468: Frank Henenlotter's Basket Case Trilogy
469-471: Hrafn Gunnlaugsson's Raven Trilogy
472-474: Fernando Di Leo's Milieu Trilogy
475-477: Nikita Mikhalkov's Burnt by the Sun Trilogy
478-480: Ousmane Sembene's Rebel Trilogy
481-483: Hirokazu Kore-eda's Family Values Trilogy
484-486: Shinya Tsukamoto's Tetsuo Trilogy
487-489: Keishi Otomo's Rurouni Kenshin Trilogy
490-492: Federico Fellini's Trilogy of Loneliness
493-495: Jia Zhangke's Hometown Trilogy
496-498: Christian Petzold's Trilogy of Love in the Time of Oppressive Systems
499-501: Hal Hartley's Long Island Trilogy
502-504: Hal Hartley's Henry Fool Trilogy
505-507: Frantisek Vlacil's Medieval Trilogy
508-510: Otakar Vavra's Hussite Trilogy
511-513: Jean Renoir's Trilogy of Spectacle
514-516: Alan Pakula's Paranoia Trilogy
517-519: Ingmar Bergman's Faro Trilogy
520-522: Celine Sciamma's Coming of Age Trilogy
523-525: Mohsen Makhmalbaf's Poetic Trilogy
526-528: M Night Shyamalan's Eastrail 177 Trilogy
529-531: Mark Donskoy's Maxim Gorky Trilogy
532-534: Jacques Becker's Paris Youth Trilogy
535-537: Lucrecia Martel's Salta Trilogy
538-540: Richard Lester's Musketeers Trilogy
541-543: Metin Erksan's Property Trilogy
544-546: Omer Lutfi Akad's Migration Trilogy
547-549: Nuri Bilge Ceylan's Provincial Trilogy
550-552: Dervis Zaim's Traditional Turkish Arts Trilogy
553-555: William Lustig's Maniac Cop Trilogy
556-558: Nicolas Winding Refn's Neon Trilogy
559-561: Nobuhiko Obayashi's Onomichi Trilogy
562-564: Aleksandr Sokurov's WWII Leaders Trilogy
565-567: Quentin Tarantino's Revisionist History Trilogy
568-570: Sergei Eisenstein's Revolution Trilogy
571-573: Vishal Bhardwaj's Shakespeare Trilogy
574-576: Pedro Almodovar's Directors Trilogy
577-579: Ruggero Deodato's Cannibal Trilogy
580-582: Aki Kaurismaki's Finland Trilogy
583-585: Axel Corti's Where To and Back Trilogy
586-588: Sean Baker's Sex Worker Trilogy
589-591: Yuliya Solntseva's Ukrainian Trilogy
592-594: Zack Snyder's DC Trilogy
595-597: Antonio Margheriti's EuroWar Trilogy
598-600: Martin Scorsese's Trilogy of Faith
601-603: Terrence Malick's Weightless Trilogy
604-606: Ang Lee's Father Knows Best Trilogy
607-609: Kenji Misumi's Sword Trilogy
610-612: Nobuhiko Obayashi's Anti-War Trilogy
613-615: Richard Sidey's Speechless Trilogy
616-618: Barbara Hammer's History Trilogy
619-621: Robert Altman's Gothic Trilogy
622-624: Joachim Trier's Oslo Trilogy
625-627: Francis Veber's Richard-Depardieu Trilogy
628-630: Marilou Diaz Abaya's Feminist Trilogy
631-633: Yoji Yamada's Samurai Trilogy
634-636: Paul Schrader's Man in a Room Trilogy
637-639: Pablo Larrain's Pinochet Trilogy
640-642: Margarida Cordeiro and Antonio Reis Trilogy
643-645: Jan Schmidt's Adventure Trilogy
646-648: Kevin Smith's Clerks Trilogy
649-651: Jean-Luc Godard's Trilogy of the Sublime
652-654: Laura Poitras' 9/11 Trilogy
655-657: Wang Bing's Youth Trilogy
658-660: M Night Shyamalan's Terror Trilogy
661-663: Soi Cheang's Monkey King Trilogy
664-666: Pablo Larrain's 20th Century Women Trilogy
667-669: Dag Johan Haugerud's Sex Dreams Love Trilogy
670-672: Tarik Saleh's Cairo Trilogy
673-675: Hiroshi Shimizu's Beehive Trilogy
676-678: Laurence Olivier's Shakespeare Trilogy
679-681: Akira Kurosawa's Shakespeare Trilogy
682-684: Roberto Rossellini's Solitude Trilogy
685-687: Sergio Corbucci's Mud and Blood Trilogy
688-690: Basu Bhattacharya's Marriage Trilogy
691-693: Bernardo Bertolucci's Oriental Trilogy
694-696: Martin Scorsese's Greed Trilogy
697-699: Fatih Akin's Love, Death, and the Devil Trilogy
700-702: Mabel Cheung Yuen-Ting's Migration Trilogy
703-705: Luis Bunuel's Search for Truth Trilogy
706-708: Elio Petri's Trilogy of Neurosis
709-711: Jonas Carpignano's Calabrian Trilogy
712-714: Alice Rohrwacher's Trilogy of the Past
715-717: Fabrice du Welz's Ardennes Trilogy
718-720: Vivek Agnihotri's Files Trilogy
The order of the list is almost random right now, I might try to find some more logical order later. Suggestions and corrections welcome!