Characters in the Animorphs world are very easily divisible into two basic categories: those who are Animorphs, and those who aren't. However, for purposes of this discussion, we will be considering several different categories and cross-categories, as you shall see.

Animorphs

• Jake
• Rachel
• Tobias
• Cassie
• Marco
• Aximilli-Esgarrouth-Isthil (Ax)

Auxiliary Animorphs

• Collette
• Elena
• James
• Judy
• Julio
• Kelly
• Tuan/Timmy
• Tricia
• VariousAuxAnimorphs
• TenUnnamedAuxAnimorphs (? The page exists, anyway.)

Other Morphers

• Alloran-Simtur-Corass (or Visser Three)
• Andalites
• AntCassie
• Arbat-Elevat-Estoni
• Arbron
• BuffaHuman
• Elfangor-Sirinial-Shamtul
• Estrid-Corril-Darrath
• Gafinilin-Estrif-Valad
• LoRren
• Tom Berenson
• Yeerks

NothLit s in one time-line or another and (form)

• Tobias (red-tailed hawk)
• David (rat)
• Arbron (Taxxon)
• Elfangor (human)
• Aftran (humpback whale)
• Aldrea (Hork-Bajir)
• Cassie (butterfly)
• large number of unnamed Taxxons (anaconda/various other snakes)

Parents of Animorphs, by Animorph

• Marco: Jeremy, Eva, Nora (stepmother, apparently abandoned to the Yeerks in favor of Eva - see also: Visser One )
• Jake: Steve Berenson, Jean Berenson
• Rachel: Naomi, Dan
• Cassie: Michelle, Walter
• Tobias: Elfangor (see also: Al Fangor), Loren
• Aximili: Noorlin-Sirinial-Cooraf, Forlay-Esgarrouth-Maheen

Siblings of Animorphs, by Animorph

• Marco: none
• Jake: Tom Berenson
• Rachel: Sarah, Jordan
• Cassie: none we know of, although she does claim to have a niece in Follow-The-Rachel
• Tobias: none, unless you're talking to one those awful fanfiction authors who thinks he's got a long-lost, incredibly hot, smart, funny, sarcastic twin sister
• Aximili: Elfangor

Obnoxiously Powerful Beings and (powers)

• Crayak (can destroy galaxies apparently at will; manipulates universe as he sees fit, bound only by the rules of "the game")
• Ellimist (can destroy galaxies apparently at will; manipulates universe as he sees fit, bound only by the rules of "the game")
• The One (assimilates. Think Borg. Also, some fans don't really believe in The One and instead suggest that he/she/it is a gigantic cop-out on the author's part, and/or a form of Crayak)

characters favored by powerful beings and occasionally granted (special powers)

• Tobias Ellimist (can morph from his nothlit form, including to his former human form; possibly given memories of his alien father)
• David Crayak (gets to torment Rachel; probably promised a lot more than received)
• Rachel Crayak (complicated relationship; Crayak promises Rachel all sorts of stuff in exchange for Jake's life)
• Elfangor Ellimist (allowed to return to his AndaLite body after becoming a Human nothlit, morphing ability apparently intact; allowed to have son via - in altered timeline - immaculate conception)
• Howlers Crayak (favored creation; amused by causing wanton destruction until Jake fixes them)
• Iskoort Ellimist (represent hope for Yeerks)
• JaraHamee Ellimist (saved from life as a Controller to found a free Hork-Bajir colony)
• KetHalpek Ellimist (saved from life as a Controller to found a free Hork-Bajir colony)

characters on powerful being's shitlist and (possibly why)

• Jake Crayak (is a cool guy and 'retrained' the HowLers; other reasons, but unknown, or at least unclear)
• Elfangor Crayak (this is up for debate, but if Crayak hates Jake, he probably isn't fond of Elfangor, either)
• Crayak Ellimist (wanton destruction of large swathes of universe)

YeerkPeaceMovement members

• Aftran
• Illium
• Cassie
• various others

Bad Guys, listed by common name/title

• Visser One (see also: Eva)
• Visser Three (see also: Alloran)
• Visser Four
• ((that one Andalite on Leera))
• ((most of the Andalites in TheArrival))
• Crayak
• The One

Prominent HumanControllers

• Tom Berenson
• Hendrick Chapman

Free Hork-Bajir

• Jara-Hamee
• Ket-Halpak
• Toby-Hammee
• various others