Broly is a light-skinned Saiyan with dark eyes and black spiky hair reaching his mid-back with short bangs framing his forehead. When he was a kid, he wore a black one-strap tunic with gray pants and brown boots, alongside a rope belt and bracelets. As an adult, Broly is very tall with a lean but well-built frame. His facial expression, even before wearing the crown, had a melancholic demeanor to it. He is shirtless while wearing white pants with a red sash draped around his waist and secured by a yellow belt with a blue gem-center. He also wears similar yellow boots with a blue gem at the top the front. It is implied that the outfit was made of a similar material to the Battle Armor, regardless of what size-increasing transformation he used, his clothing always remained intact and grew in size with him.
To better control Broly and his power as his mental-instability continued to grow, Paragus placed a crown on Broly's forehead, along with wristbands and a necklace with a flat plate over the chest, each which are golden with a blue gem. Broly also wore golden bands over his biceps. After breaking free from Paragas' control, Broly's crown and armbands were destroyed. After Broly's defeat against Goku, he obtained scorch marks across his chest.
When first seen, Broly is seen as a rather docile and harmless-looking Saiyan (uncharacteristic of a majority of the Saiyan race). However, Broly has a dual nature, as indicated in Paragus's flashback, when he briefly wakes up and calmly asks what Paragus is up to, only to end up going into a screaming fit when realizing that Paragus is about to place the mind-control crown on his head. Once shifting into his more aggressive state, Broly demonstrates his love of fighting and brutality just like the typical Saiyan, but on a far more destructive level. This violent and maniacal side of him seemingly stemmed from both his extraordinary power that he never properly learned to control as well as the traumatic events of his birth, causing his frenzies to happen more frequently and last longer as he grew. Largely because of his insanity, Broly was also known to get hysterical when causing destruction or going into a frenzy, such being especially evident in Paragus's flashback where Broly after destroying a cityscape as a child is seen laughing uncontrollably, even while being physically restrained by Paragus. Broly also seems to have a real problem controlling his rage, meaning that he could end up destroying himself. In an effort to control his erratic behavior, Paragus used a device to subdue Broly's temperament.
When free of Paragus's control device, Broly's Saiyan nature becomes dominant. His thirst for combat and desire for death and destruction of things is unyielding, as shown by his destruction of Planet Shamo. Broly seems to acknowledge his malevolence; Piccolo calls him a freak, to which Broly replies that he actually is a devil (the FUNimation dub for the film tones this down slightly while at the same time getting the implications across by having Piccolo in the aforementioned scene accusing Broly of attacking children first in a disgusted tone, as well as Broly responding that he merely does what is needed to be done, before telling him that the Namekian should have expected that from "a true freak."). It is suggestive that even though Broly was driven mad with his birth-given power and the various circumstances of his birth, Broly has some sanity of said madness as he has also shown some intelligence while on his rampage: he sees through Paragus' lies and plan for having him die in the planet's collision with Comet Camori, as well as briefly engaging in ambushes against Gohan, Goku, and Future Trunks within the ruined city and successfully catching them off guard, and also deducing right before his first defeat that Goku's increase in power had been due to donations from his allies. A similar display of intellect was also demonstrated in the Victory Mission manga, where he, in a similar manner to King Piccolo, proceeded to devour two Dragon Balls in front of Beat and Froze, and then forces them to fight against him, knowing full well they can't actually harm him. Also (in the FUNimation dub at least), he has a very dark sense of humor: When Goku demanded a handicap during the fight, Broly proceeded to sadistically ask him if "handicap" is another word for a coffin. He also had a more sarcastic sense of humor, at least in the Funimation dub, such being evident before he destroyed Planet Shamo, where he remarked that the Shamoian slaves decided to show bravery despite their being huddled together in complete fear at the time. He also seems to have some degree of respect for fighters who attempt to stop him even when the odds are against them, as evidenced by his remark to the Z Fighters in the Japanese version where he even claimed they were very much worthy of their Saiyan blood (in the FUNimation dub, he says the opposite: he instead calling them wastes of Saiyan Blood). Similarly, he seems to have some loathing of fighters who were all talk and no action, as evidenced by his remark to Vegeta shortly after he ended up quickly defeating them where he called him a "true piece of trash." Although largely lacking self-restraint, he nonetheless was implied in the Japanese version to hold just enough to hold off destroying New Planet Vegeta to allow Goku and the other Z Fighters a chance to fight with everything they had (although this was mostly because his Saiyan instincts demanded him to have a fight).