Baby

Look. Look. The Baby Saga of Dragon Ball GT is the most fun I've ever had watching an anime. I like this funky blue slime dude.

As taken from the Dragon Ball Wiki:

"Baby is from a far away galaxy. During the Saiyan-Tuffle war, the last of the Tuffles created genetically superior life forms, parasite-like organisms, which they infused with the DNA of the Tuffle King. These organisms were spread throughout the universe around Age 730, with the overall goal to destroy the Saiyans in revenge for the destruction of the Tuffles by King Vegeta and his Saiyan forces. Baby was the first Tuffle parasite to return and try to obtain vengeance against the Saiyan race. While drifting through space, at Age 735, Baby swears vengeance against the Saiyans for wiping out the Tuffles and furthermore devises the "Universal Tuffleization Plan" in order to revive the Tuffles. In Age 740, Baby manufactures Dr. Myuu in order to gather the resurrection energy he needs to obtain a powerful body. Baby programs Myuu with the method of developing Machine Mutants, and production began on Luud, M-2, and the others. Seemingly created as a "last resort" by the demented Machine Mutant Dr. Myuu, Baby is a parasite whose purpose for living is to see through the annihilation of the Saiyan race and domination of the universe in the name of the Tuffles. However, as his name implies, Baby is highly immature and is prone to fits of rage and panic, as well as not taking his battles seriously. It is also implied that "Baby" was not his original name, or at least that this is not what he was intended to be dubbed, as Baby does not initially recognized the titled and begins to dislike it. During the battle between the Baby-possessed Gohan and Goten against Vegeta, Baby reveals to Vegeta his true Tuffle background and how he was created."



I still think it's hilarious that the best villain in GT was named Baby