Sho Fukamachi was an ordinary high-school student with no real worries beyond moving along in school and trying to catch the eye of Mizuki Segawa, the younger sister of his best friend, Tetsuro Segawa. That is, until he witnessed an explosion on a nearby mountain and came across a mysterious artifact which granted him the power to summon a suit of Bio-Boosted Armor called the Guyver. An evil corporation, Chronos, lost that Guyver unit in the explosion that Sho witnessed, and will go to any lengths, using any underhanded measures, to get it back. Using their army of modified humans (called Zoanoids, capable of transforming into monstrous forms with increased speed and strength, and occasionally other enhancements), and even the second Guyver unit still in their possession, Chronos attempts to regain possession of the Guyver which has bonded itself to Sho.
Originally a manga by Yoshiki Takaya, which began running in 1985 and is still currently serialized. 31 volumes have been published so far.
There have been several Fanfiction stories dedicated to this series, though the fandom itself remains rather small and cultish, and also a fully-independent Fan Verse called Warrior Guyver, as well as a more closely-interwoven 'Verse called Son of Mine.
Canon
Zoalords
Alkanphel (Archanfel)
Hamilcal Balkus (Hamilcar Barcas)
Waferdanos ("Walter Daniels")
Shin Rubeo Amniculos (Sin)
Fried'rich van Purg'stall (Pulukshterl) ("Paul Kushtar")
Edward Caerleon
Li Yentsui (Rienzi)
Luggnagg de Clumeggnic (Kurumeggnik) (Krumeggnik)
Tuaha De Galenos (Tuarhan)
Jabir Ibn Hayyan (Jaervill Bun Hiyern)
Cablarl Khan (Kabral) (Kaburaal)
Richard Guyot (Reholt Gyou)
later Imakarum Mirabilis
Hyper Zoanoids
Zektor (Zx-Tole)
Elegen
Gaster
Darzerb (Derzerb)
Zancrus (Thancrus)
Myumelzee
Noskov
Zerebubuth (Zerabubuse)
Zangallo
Billbo-Negg
Zencrebe
Bilifinger
Danaplus
Minodlius
Gustav (prototype)
Zoanoids
Gregole
Ramotith (Ramochis)
Cadan
Brelimos
Vikarr
Devold
Casvarius
Valvatos
Vamore
Bystoma
Gernold
Gepatolls
Razell
Neagle
Citiciss
Curvill
Lu-kill
Geefog
Gobilva
Broiz
Tabross
Golvarun
Lost Numbers
Aptom
Somlum (Samarubu)
Dyme (Dymu)
Gelpess
Guyver Killers
Enzyme
Enzyme II
Enzyme III
Other Zoaforms
Arlen Crane
Gus Volker
Markus Edwards
Lisker
Guyvers
Sho Fukamachi / Guyver I
Agito Makishima (Makashima) / Guyver III
Oswald A. Lisker (Risker) / Guyver II
or
Valcuria / Guyver II
Valkyria Fosberg-Lisker / Guyver II Female
Sean Barker / Guyver "US"
⬅ Tyler
Guyver allies
Toshiaki Hayami / Bio-Freezer
Aptom
Dr. Alfred Hekkaring
Shizu Onuma / Griselda
Yohei Onuma
Masaki Murakami
Atkins (Aiden)
Max Reed
Natsuki Taga
Shiyu Odagiri (Sumio)
Shinichiro Yamamura
Tetsuro Segawa
Mizuki Segawa
Aso Keisuke
Tokiwadaira Tamotsu
Cori Edwards
Other Characters
Advents
Apollyon (Apollon)
Genzo Makishima
Fumio Fukamachi
Locations
Shinjuku
Colorado
Los Angeles
Setageya
Chronos Bases
Arizona Base One
Cloud Gate
Dead Sea Plant
Pillars of Heaven
Mt. Minakami / Relic's Point
Other Locations
Relic
Ark
Silha
Odagiri's mansion
Guyver Characters (fanon)
Adaptation ('verse)
Lord Xerxes/ Second Zoalord of the Council
Neo-Zector
Neo-Derzerb
Neo-Thancrus
Neo-Gaster
Neo-Elegen
Dr. Ichimaru
Warrior Guyver
Destrol
Cyber Guyver
Son of Mine ('verse)
Ryan Crouger / Guyver V
Kenji Murakami / Ingriam Mirabilis
Dr. Simon Sanderson
Dr. Edmund Halverson
Dr. Hedrick Henderson
Dr. Howard Jackson / Felinos
David Drake
Drake Shepherd
David Grayson
Daniel Evans
Daniel Morrison
Dr. Graymalkin
Larry Henderson
Dr. Lloyd Asplund
Norman Crouger
Norma Crouger
Dr. Danielle Sorenson
Female Zoanoids (I.S.F.)
Sharru
Ranza
Cassica
Chaltu
Javisis
Samarubu (Lost Number)
Standard Zoanoids
Maldu
Chaldu
Davu
Dual Life Refraction
Imakarum "Hikari" Mirabilis
Akane Makishima
Yukari Fukamachi / Isis Mirabilis
Other Fan Characters
Notable Guyver Fanfiction
Son of Mine series
Son of Mine
Brother Mine (sidestory)
The Birth of Guyver V
Meeting Places
Days of Fire and Thunder
The Stranglehold Protocol
More Information
Wikipedia's article on the Guyver manga
Wikipedia's article on the 2005 TV series
Wikipedia's article on the 12 part OAV
Wikipedia's article on the first OAV
Guyver Solution
Contains information and character profiles for all three iterations of the story.
Guyver World — Russian fansite and database.