There are a lot of characters that make copies of their self similar to Naruto which was already mentioned. I'll contribute Gemini Man from Mega Man 3 and Steve Urkle from Family Matters. There are also some that break into pieces and do things separately.

Unless it's a single computer directly controlling many, artificial intelligence should be excluded. Clones as well, as they are pretty much the same thing, just flesh. It would be no different then someone who sets up (bad program) on several computers then says they 500 box wow. This would disqualify both Urkle and Naruto, and I'm not sure about Gemini Man or Smith.

The puppet controllers from Naruto would qualify as boxers.

The borg isn't a boxer, it's a pug. A really, really big one.