The story
From little + blue + man. Coined by Andrew S. Erickson of the Naval War College by analogy with little green man, Russian covert soldiers deployed during the 2014 annexation of Crimea.
Etymology from Wiktionary, CC BY-SA 4.0.
little blue man
Today it means: A member of the Maritime Militia of the People's Republic of China, primarily operating on fishing and motorboats, who aid in the pursuit of its maritime interests in disputed waters (and especially those relating to the territorial disputes in the South China Sea); chiefly when viewed as a covert projection of power, intended to encroach on the sovereignty of other countries. Full definition →