Out of the two Bud is the less sociable of the pair and grumpy. He dislikes people other than members of the King family around him and will often growl (and sometimes attack) those who annoy him.
Lou on the other hand loves getting attention from people and will be very playful around Alien's friends. However he is still very destructive like his brother and will attack people if given the command.
One day when Alien-king was surveying a hive in a local colony he came across a zoo, he decided to take a look out of curiosities sake. Most of the animals there were killed by other xenomorphs from his hive however when he was about to leave until he heard whimpers coming from inside. He followed noises until he reached a cage, there was a dead spotted hyena mother and beside her was two pups he just kept looking at them wondering what to do until he heard something else. There were three xenomorphs entering the zoo when they noticed the pups they went to attack them but Alien defend the pups and killed the other xenomorphs. From that day on Alien raised them. And being a fan of comedy he decided to name them after the two comedians, William 'Bud' Abbot and Lou Costello who he would often watch on cold colony TVs.
Bud and Lou were first met by the Adventure Group when Alien move into Blair's house where they started destroying furniture which made Alien have to look for his own home. When Alien, Marq and others went to Skyverse Bud and Lou joined and were present when the NDE attacked the Skyverse capital. They took part in many other adventures when they weren't living in Alien's warehouse.
After Alien hatched from his cocoon and turned fully into the Xenomorph king he left to become leader of his home hive. Bud and Lou lived with him at the hive, Alien warned his hive that if they ever come to harm, he will single handedly destory the hive. Of course he would never actually do this but this threat alone kept them safe.
Now Bud and Lou stay at Alien and Helenna's home, helping look after Amber and Carmen even though they seem to cause even more destruction now with Carmen's influence.