The son of a Jew of Berlin and of a Dutch Protestant, Justus Hafner was inscribed on the civil state registers as belonging to his mother's faith.

But the latter died when Justus was very young, and he was not reared in any other liturgy than that of money.

From his father, a persevering and skilful jeweller, but too prudent to risk or gain much, he learned the business of precious stones, to which he added that of laces, paintings, old materials, tapestries, rare furniture.
An infallible eye, the patience of a German united with his Israelitish and Dutch extraction, soon amassed for him a small capital, which his father's bequest augmented.

At twenty-seven Justus had not less than five hundred thousand marks.

Two imprudent operations on the Bourse, enterprises to force fortune and to obtain the first million, ruined the too-audacious courtier, who began again the building up of his fortune by becoming a diamond broker.
He went to Paris, and there, in a wretched little room on the Rue Montmartre, in three years, he made his second capital.