Saiyans

"'"Saiyans (サイヤ 'Saiya-jin') are a race of extraterrestrials in the anime and manga Dragon Ball and its adaptive sequels, Dragon Ball Z, Dragon Ball GT and Dragon Ball Super. In the series, the Saiyans from Universe 7 are a naturally aggressive warrior race who were supposedly striving to be the strongest warriors in the universe

In Dragon Ball Super Z, Saiyans are common on earth, even though they have no knowledge of being Saiyans. Normally, Saiyans are sent to planets to destroy, and take them over, while the kids go to weaker planets and do the same as adults, but for Earth they decided to send a bunch of pods, all of which successfully make their way to earth.

When these Saiyan children landed on earth, they of course did what they were supposed to, and destroyed everything. This kept going on, for weeks, months, until finally, all of the children one by one kept somehow hitting their heads, making them more docile.

Even though the Saiyans are no longer a threat normally, every full moon they transform into something called the 'Great Ape' or Oozaru transformation. The only way to defeat one of the Great Apes, is to either cut off the tail, or destroy the moon, if you can't do either of those things you must kill the Saiyan. All of the Saiyans sent to earth, currently live a normal life as a Human. Any other Saiyans, are doing what Saiyans normally do, which is destroy planets and then sell them.