Before Dragon Ball Z: Battle of Gods became a reality...

[Steven Bloodriver]

Were there any villainous characters able to challenge Super Saiyan God?

[Dbzfan94]

Well didnt the original Super Saiyan God fight the evil Saiyans or something like that??

Goku was the first SSJG since then

[Bullza]

I think he ended up losing because his time ran out is all.

Also the strength of Super Saiyan God depends on who becomes it so if the previous Saiyan who became it had a power level of a few thousand whereas Goku's was dozens of millions probably, then the original Super Saiyan God likely wasn't anything like what Goku was.

[nickzambuto]

Maybe some movie villains? Like Janemba and up. The movies were always more powerful than the main series, what with Broli destroying a quadrant of the universe and SSJ3 Goku shaking the whole afterlife.

[Zephyr]

If you wanted to include GT, I think the only loose connection you could make is for Super Saiyan 4 to be somewhere in Super Saiyan God's ballpark (by way of both being loosely comparable to Super Saiyan Vegetto). From there, you could argue that anyone stronger than Super Saiyan 4 Goku during the fight with Baby would be able to beat Super Saiyan God. So I think that would be Golden Ozaru Baby, Super 17, and Yi Xing Long?