Who discovered the Saiyan forms?

[Yuji]

We're aware that Oozaru, Super Saiyan and Super Saiyan God all have precedents in ancient Saiyan lore. Likewise, we can infer with some degree of logic that Golden Oozaru and Super Saiyan 4 had probably been achieved by the ancient Saiyans at some point, since the only apparent requirements to achieve the form are a tail and being a Super Saiyan. What about the other forms, however?

In the series itself, the first Saiyan to ascend past Grade 1 was Vegeta, who developed Grade 2 (and is implied to have either achieved, or had knowledge of how to achieve, Grade 3). Gohan then surpassed him with Super Saiyan 2, and Goku a few years afterwards with Super Saiyan 3. Finally, Super Saiyan Blue was achieved by Goku and Vegeta at the same time. The first Super Saiyan God died without controlling the form, so it seems likely that the first time we see Super Saiyan Blue in the series itself is also the first time the form has ever been used in-lore. But as for the other forms, that seems less possible to ascertain.

Do you reckon any of the forms above may have been discovered or created by Saiyans prior to our main cast?

[nickzambuto]

I think you summed it up. Super Saiyan 1 and Super Saiyan God were achieved many years ago by unknown saiyans, but nobody ever ascended passed those states because they both died soon after transforming.

Vegeta was the first person to ascend passed Super Saiyan in any way, then Gohan created SSJ2 and Goku created SSJ3, and Goku and Vegeta together created Super Saiyan Blue.

Goku also probably created Super Saiyan 4. It's possible that a Golden Oozaru appeared before him, but it seems unlikely that another saiyan would be able to control that form and evolve to Super Saiyan 4. Goku was pretty unique for doing that.

[precita]

Super Saiyan 3 feels like it's an off-shoot form only discovered by Goku and then Gotenks was able to repeat it. Super Saiyan 2 is simply the original Super Saiyan used to its full potential.

[Polyphase Avatron]

I assume Oozaru was discovered the first time a Saiyan with a tail looked at a full moon.

SSJ1 and Super Saiyan God was discovered by Yamoshi.

[Yuji]

I assume Oozaru was discovered the first time a Saiyan with a tail looked at a full moon.

SSJ1 and Super Saiyan God was discovered by Yamoshi.

Actually, the original Super Saiyan and Super Saiyan God were different people. The original Super Saiyan was (presumably? Toriyama never specifies if he was the first) Yamoshi back in planet Sadla, whereas the original Super Saiyan God was born on planet Vegeta; the Super Saiyan God becomes possible because Yamoshi's spirit wanders the mortal realm seeking righteous Saiyans to avenge him.

[PerhapsTheOtherOne]

I assume Oozaru was discovered the first time a Saiyan with a tail looked at a full moon.

SSJ1 and Super Saiyan God was discovered by Yamoshi.

Actually, the original Super Saiyan and Super Saiyan God were different people. The original Super Saiyan was (presumably? Toriyama never specifies if he was the first) Yamoshi back in planet Sadla, whereas the original Super Saiyan God was born on planet Vegeta; the Super Saiyan God becomes possible because Yamoshi's spirit wanders the mortal realm seeking righteous Saiyans to avenge him.

Precisely this. It's still baffling to see people get confused at this even to this very day.

=

Anyways, as to the OP, the legendary Super Saiyan was so rare to achieve that almost no one could've really had a chance to experiment and expand on it and related forms' power. Mainly because, well..... they were all dead.