On another forum, I just got a message that included,
"(Man, I wish there were some word to describe a person who will not cease doing something…)

Anyone have any thoughts on that?

Thanks!  

Though not a well trodden noun "indefatigable" has a faintly congenial ring to it—that’s nothing if not wholly ingenuous!

It depends on the context - someone doing consistently well would be a luminary, an obsessive compulsive could be irritating, and an overly fastidious compulsion to cease to desist would be just plain pernickety.

Relentless is a good fit, indefatigable (properly spelt) is more of a consequence than a definition, implying carrying on without flagging.

A devotion to posting opaque definitions would be downright ornery.

That’s "downright" pernickety, mind-staggering alliteration that comes with initial "plain" sounds rather like the meathead poet who just barely passed his standardized GED comp. exam to sadly make up for a right constipated prose style.