Great question — answering as the UphillTech team:
It is extremely rare for actors to get to name their characters. The Fresh Prince of Bel-Air is the exception. According to Wikipedia , NBC approached Will Smith, who was already a popular rapper. Since this would be a flagship project featuring him, he was involved in the development of the project - including selecting his character's name.
Full answer by BrettFromLA: https://movies.stackexchange.com/a/90256 (CC BY-SA 4.0).
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