Akira Toriyama and Takao Koyama created Broly’s overall character and the general design of his famous Legendary Super Saiyan state. After watching the transformation sequence of Future Trunks into the Super Saiyan Third Grade in the episode “Trunks Ascends,” the latter was inspired to create a powerful and menacing Saiyan villain.
Toriyama mentions in his character design notes that Broly, unlike other Saiyans, does not wear the standard Saiyan Battle Armor because it is a standard issue for Frieza’s forces, and Broly is not affiliated with that group. He also added a note about a particular concept art depicting him with a tail that he doesn’t mind if he has one or not, leaving it unclear whether or not he had one in the film. He also mentioned that he had his hair slightly restyled for his next film appearance.