Rumor Guide - Who Designed Super Saiyan 4?

Kanzenshuu provides the back history, context, and facts surrounding Super Saiyan 4's design by Katsuyoshi Nakatsuru (not Akira Toriyama!)

Dragon Ball AF Explained

Why does everyone have such a problem with the idea of Super Saiyan 4 being as powerful as a Super Saiyan God Super Saiyan? - Quora

Dragon Ball Reveals New Super Saiyan 4 Form

Databook Guide, Daizenshuu Volumes

Dragon Ball: Every Saiyan, Ranked By How Hard It Was For Them To Turn Super Saiyan

Dragon Ball AF Explained

Dragon Ball GT: S.H. Figuarts Super Saiyan 4 Vegeta Official Images Revealed - ORENDS: RANGE (TEMP)

Dragon Ball AF, Dragon Ball Wiki

Rumor Guide - Goku Being An Alien Is Foreshadowed

Goku's New Super Saiyan Form Officially Confirmed

Why Dragon Ball GT's Super Saiyan 4 Actually Matters

What To Expect For The Upcoming 'Dragon Ball Super' Arc

Dragon Ball Super Season 2 Release Date Rumors: Is It Coming Out?

The 10 Best Dragon Ball Z Characters - IGN

How a Super Saiyan 5 fan-art hoax transformed the Dragon Ball franchise - Polygon