Ultra kamehameha is a attack invented by Vetio. When Vetio used the kamehameha, he was using pure anger
451px-Ultimate flare
which triggered him to use the ultra kamehameha. Instead of being blue, it could be black or a light yellow and it is about 25 times stronger then a normal Kamehameha. Vetio became known to use this attack. Even Vegeta copied the move. In order to have the power to use the Ultra Kamehameha, you have to be a Super Saiyan 3 and block off pure goodness you must use hatred. The Ultra Kamehameha was known to be a Legendary move so great not even Goku could learn it. Only the greatest fighters could learn it only Vegeta and Veito know this move. It turns out Vekau also learned this move, but claims to have made it. Vekau's Ultra Kamehameha is only 20 times more powerful then a normal Kamehameha.