Is there a specific word for when somebody creates a fictional character who is very obviously another more famous character with a slightly different name and a few tweaks to avoid breaching copyright laws? 

For example, if I wrote a comic book about a character called Ultraman who wore a blue and red suit with a cape and a big U on his chest; and who could fly, was super strong, super tough, had laser vision, etc. Obviously Ultraman is Superman. 

Is there a specific word for characters like this? I know that TvTropes called them "Captain Ersatz" but I'm wondering if there's a more formal dictionary approved word.