The story
Coined by Geoff Fraizer and Greg Boyko, who played the online multiplayer game Warcraft II: Tides of Darkness under the names Shlonglor and Warp. The pair had become so proficient at the game that few people would play against them, so, in order to avoid scaring off potential competitors, they created alternate accounts named PapaSmurf and Smurfette (characters from the Smurfs comic franchise). Smurf account as a banking term, however, predates Warcraft II by about a decade.
Etymology from Wiktionary, CC BY-SA 4.0.