I'd never thought about it before, but its Communist usage does seem to have started as a Russian thing, presumably reflecting the party's illegality, perhaps as a safeguard against police infiltration of party cells: I can use my name in everyday life, but within the Party I'm such-and-such - let the authorities hunt him instead. Prominent German Social Democrats conversely tended to use their "real" names even during the period of repression (1878-90), but they enjoyed some freedom in electoral activity.

Pseudonyms had of course been used in writings in the past - American revolutionary authors routinely adopted Roman ones, and even innocuous British tracts might be credited to "A Merchant", "A Lover of His Country", etc, but such names existed merely on paper rather than in their political life.