Bulma Briefs Enemies

At first they were enemies because, Android 18 was programmed by Dr. Gero, who was an evil man that was a member of the red ribbon army, that was a sworn enemy of goku. It was android 18, 17 and 16 who were made to kill goku and all who support goku. However, android 18 changed her ways and then became good friends with android 18 who married krillin. In another reality, Android 18 was cold blooded and killed humans for fun, this angered Bulma and her son Trunks, in that reality, android 18 never turned good. Hence they were always enemies.

A parasite who desires nothing more than to see the destruction of all Saiyans

An evil dragon that is summoned by the Blackstar Dragon Balls.

Cell dubbed The Perfect Warrior is an Android of great power who possesses all the cells of the greatest fighters of all time

Mad Scientist of Dragon Ball Z.

The intergalactic tyrant who destroyed Planet Vegeta along with almost the entire Saiyan race.

Was a part of the red ribbon army which was a group that were enemies with her and goku, they fought constantly, and with goku to protect her, they defeated the red ribbon army. Bulma even tried to seduce general blue but it failed as he was focused on his evil goal.

Leader of the Ginyu Force.

Also known as Demon King Piccolo, He is the Evil half of Kami.

In DragonBall Evolution (2009), lord Piccolo was more like Piccolo Daimao and Piccolo Jr combined. He also lacked a "good half" (Kami-sama). Lord Piccolo didn't seek for youth- he was young already. After being defeated by Goku he called himself "Neo Piccolo", dressed in all red.

Buu is one of the strongest fighters that Goku has ever faced. Don't let the pink skin and lack of ears fool you he has power beyond that of many of the DBZ fighters.

Maron was a minor character in Dragonball Z that served the purpose of providing fanservice, and little to nothing more.

An old enemy of Goku who tries to find the Dragonballs. He is also the first person to use the Blackstar Dragonballs, though he did so by mistake.

Goku's older brother in the Dragon Ball Z series. Came to Earth and kidnapped Gohan to blackmail Goku into joining him.

One of Pilaf's faithful followers.

He is the most powerful dragon in Dragonball GT and he is destroyed by Goku with his ultimate spirit bomb(universal Genki Dama)