Answer:
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Ninja
Master Wu (Lloyd's uncle/Master of Creation/Dragon Master/mentor and founder)
Master Lloyd Garmadon (Green Ninja/Master of Energy/Golden Ninja/former Master of Golden Power/leader)
Kai (Red Ninja/Master of Fire)
Jay Walker (Blue Ninja/Master of Lightning)
Cole (Black Ninja/Master of Earth)
Zane (White Ninja/Titanium Ninja/Master of Ice)
Former
Nya (Water Ninja/Master of Water; merged with the Endless Sea)
Master Garmadon (Lloyd's father/Master of Destruction and Creation/mentor; turned evil again)
Allies of the ninja
Misako Montgomery Garmadon (Lloyd's mother/archaeologist)
P.I.X.A.L. (Samurai X/Cyrus Borg's "daughter")
Falcon (Zane's companion/communications for the ninja)
Ronin (business partner)
Dr. Julien (Zane and Echo Zane's "father"/creator; deceased)
Ed Walker (Jay's adoptive father)
Edna Walker (Jay's adoptive mother)
Lou (Cole's father)
Ray (former Master of Fire/Kai and Nya's father)
Maya (former Master of Water/Kai and Nya's mother)
Cyrus Borg (P.I.X.A.L.'s "father")
Nindroid Sentries
Sentry General (leader)
Dareth (honorary Brown Ninja)
Auto
Nelson (honorary Purple Ninja)
Jake
Mystake (deceased)
Ninjago City Police
Police Commissioner
Detective Simon
Detective Tommy
Officer Noonan
Officer O'Doyle
Officer Jimmy
Police Officer
Night Watchman
Echo Zane (Zane's "brother"/Dr. Julien's "son")
Seliel (Phantom Ninja)
Seliel's father
Phantom Ninja (non-canon)
Carridi (non-canon)
Neido (Ninja of Imagination; non-canon)
Nobu (non-canon)
Morro (Master of Wind; reformed in "Curseworld, Part II"; deceased)
Royal Family of Ninjago (dissolved)
Emperor of Ninjago (Harumi's adoptive father; deceased)
Empress of Ninjago (Harumi's adoptive mother; deceased)
Princess Harumi (revealed to be an enemy; deceased)
Hutchins (Master-at-Arms; deceased)
Royal Guards (deceased)
Master Kodokuna Yang (creator of Airjitzu; reformed in "Day of the Departed")
Milton Dyer
Okino
Scott
Racer Seven
Twitchy Tim
Elemental Masters
Past Elemental Masters
Master of Ice
Master of Gravity
Master of Sound
Master of Shadow
Unknown Elemental Master
Griffin Turner's grandparent (Master of Speed)
Cole's grandfather (Master of Earth)
Lilly (Master of Earth/Cole's mother; deceased)
Jay's mother (Master of Lightning)
Skylor's mother (Master of Amber)
Current Elemental Masters
Skylor Chen (Master of Amber; reformed in "The Forgotten Element")
Ash (Master of Smoke)
Gravis (Master of Gravity)
Mr. Pale (Master of Light)
Bolobo (Master of Nature)
Neuro (Master of Mind)
Griffin Turner (Master of Speed)
Jacob Pevsner (Master of Sound)
Karlof (Master of Metal)
Tox (Master of Poison)
Shade (Master of Shadow)
Chamille (Master of Form)
Other characters
Creator of Ninjago
First Spinjitzu Master (deceased)
Ninjago City citizens/Miscellaneous
Andrea Thomson
Announcer
Antonia
Bank Boss
Benny
Dr. Berkman
Bob Rattlebottom (non-canon)
Bob the Intern
Cathy
Cecil Putnam
Chuck (non-canon)
Circus Clown
Claire (non-canon)
Cliff Gordon (Jay's biological father; deceased)
Clutch Powers
Construction workers
Cook
Dan and Kevin Hageman
Dan Vaapit
Dwayne
Flerry McFloyster (non-canon)
The Fold
Fred Finely
Fugi-Dove
Fugi-Dove's brother
Gayle Gossip
Genn (non-canon)
Green Screen Gary (non-canon)
Grumbmiller
Hageman (deceased)
Harumi's father (deceased)
Harumi's mother (deceased)
Hibiki (non-canon)
Hiroshi
Jamanakai villagers
Jay Vincent
Jeremiah Bobblestein (non-canon)
Jesper (non-canon)
Johnny
Juggernaut
Kabuki
Korgran's father
Lar (non-canon)
Larry (Ronin's cousin; non-canon)
Leroy
Lumberjacks
Magician
May Robsen
Michael Kramer
Milton Dyer's father
Mrs. Dyer (Milton's mother)
Monks
Motorcycle Mechanic
Museum Curator
News Reporter
Ninjago soldiers
Warden Noble
Patty Keys
Percy Shippelton
Postman
Prison guards
Rachel Sparrow (non-canon)
Repo Man
Restaurant Owner
Rice farmers
Mr. Righty Tighty (non-canon)
Roise
Explanation:
much more.