In Dragon
Ball Z he is a
badass Saiyan that is spoken of in legends. He was born on the same day as kakarot (Goku) and hates more than anyone can hate anything because goku was bawling for hours shortly after being born. When Broly was born he had an insane power level of 10,000 which freaked out King Vegeta so he had the
baby killed along with his
father Paragus. Later on he met Goku again and sparked up pure
rage unleashing the legendary Super Saiyan. This freaked out Vegeta(King Vegeta's son) and refused to fight him until later on. Only using all of goku, piccolo(a green alien from planet Namek), trunks(vegeta's son) and gohan (Goku's son) were they able to defeat him but he later found out he lived in another movie and got blasted into the
sun, and also had a clone later on in another movie.
Broly scared the shit out of
Vegeta and pretty much everyone else
even his
father. He will fuck your shit up.