The most popular series of the trilogic saga. It again stars Goku and his loyal followers directly after the end of Dragonball. This time he must save the earth from various threats including his arch rival Vegeta amongst many other foes. Along with many fierce battles, this is the series where the Super Saiyan was first mentioned and seen. The first character to make this transformation was Goku.
After seeing his best friend Krillin murdered by Frieza, Goku went into a period of rage and his Super Saiyan powers were awakened. The next person was Vegeta, who was furious at himself for letting Goku surpass him. After this, many other characters made this transformation including Gohan, Goten, and Trunks. If you include the Story of Trunks special, Future Gohan and Trunks are Super Saiyans as well. The most advanced Super Saiyan form ever accomplished was SS3 (Goku). This is not the strongest transformation though, as in Dragonball GT Super Saiyan 4 is created. The 3 super-villians in the series include Freiza (killed by Goku), Cell (killed by Gohan), and [Fat/Super/Kid] Buu (killed by collective energy of Earth in Goku's Spirit Bomb).