Sophie Gräfin von Hatzfeldt, born Gräfin von Hatzfeldt-Schönstein zu Trachenberg (10 August 1805 in Trachenberg (Lower Silesia) – 25 January 1881 in Wiesbaden) was active in the German working-class movement and partner and confidante of Ferdinand Lassalle.
Ferdinand Johann Gottlieb Lassalle (born Lassal; 11 April 1825 – 31 August 1864) was a German jurist, philosopher, and socialist activist. Best remembered as an initiator of the social democratic movement in Germany, in 1863 he founded the General German Workers' Association (ADAV), the first independent German workers' party. His political theories included state socialism and the popularisation of the iron law of wages.
Born in Breslau to a prosperous Jewish family, Lassalle became a follower of Hegelian philosophy in his youth. During the 1840s and 1850s, he gained public renown for his involvement in a long and sensational legal case to vindicate the rights of Countess Sophie von Hatzfeldt. Active in the revolutions of 1848, he formed a complex and often antagonistic relationship with Karl Marx and Friedrich Engels. Lassalle also authored several major intellectual works, including the philosophical treatise Heraclitus the Obscure (1857) and the legal study The System of Acquired Rights (1861).