One of the earliest I can remember, way back from the early 2000s when I first got into the fandom and have seen repeated as recently as earlier this decade:
"Super Saiyan is based on the legend of the Golden Warrior"
I forget the site where I first read it, other than that this was around 2004. And ever since, it's actually been most religiously repeated by Sonic fans trying to explain why Super Sonic looks like Super Saiyan— a challenge that's only a thing because Yuji Naka lied and said that Super Sonic
wasn't an homage to Super Saiyan as a joke in an interview, so people tried to explain it through other means.
And it was also noted that there were other anime characters that turned gold, most notably in Saint Seiya. So at some point, someone on a DBZ fansite came up with a seemingly convincing explanation that the reason why so many Japanese characters turned gold and received major power ups was because of an ancient old legend of a "golden warrior" who attained superhuman power (and a shining golden color). Dragon Ball Z was just drawing from that myth, as was Sonic and others. I myself believed this for a good while.
In actuality, that's utter bullshit. There's no such thing as the "Golden Warrior" (at least, not until Gohan decided to bust some criminals up one day early in his high school career).
Indeed, if in the case this wasn't a lie from the start and was actually a serious attempt at explaining things, it was just a 90s mistranslation of an actual Japanese fable— that of Kintarō, aka the
Golden Boy, a tale of a boy based off someone from Heian-era Japan who apparently had superhuman strength (he admittedly shares some bare similarities with Son Goku). However, he wasn't actually gold, nor did he ever transform into a golden-haired form. And it's also come out that Toriyama made Super Saiyan gold just to make it obvious that Goku became stronger, and did it in a way that also saved ink.
This myth has been so totally
destroyed that, to my surprise, it's actually somewhat difficult to even find any references of it on Google anymore, though some results still do come up (including one linking back to Kanzenshuu).