Dietrich IX, Graf von Kleve, was born about 1291, the elder son of Dietrich VIII, Graf von Kleve, and his second wife Margarethe von Habsburg, Vrouwe van Duisburg. From 1297 he was betrothed to Margarethe van Gelre, daughter of Reinald I, Graaf van Gelre en Zutphen, and his second wife Marguerite van Vlaanderen; they married about 7 May 1305. Of their three daughters only Margarethe would have progeny, marrying Adolf II, Graf von der Mark, who had earlier been married to and divorced from her first cousin Ermgard von Kleve.
After the death of his older half-brother Otto in 1310, Dietrich succeeded with great difficulty in asserting his right to succeed him, against the opposition of a coalition of Otto's widow Mechtild von Virneburg, her grand-uncle the Cologne archbishop Henrich II von Virneburg and Graf Engelbert II von der Marck, who were pushing the candidacy of Otto and Mechtild's daughter Ermgard.
In 1318 Dietrich reached an inheritance agreement with his younger brother Johann; he gave Johann the land of Linn and assured him of the succession to the county of Kleve in the event that he himself had no sons.
Margarethe died in 1331, and in December 1340 Dietrich married Maria von Jülich, widow of Heinrich, Graf von Virneburg, and daughter of Gerhard V, Graf von Jülich, and his second wife Isabella of Brabant, heiress of Sichem, lady of Vierson. The marriage did not result in progeny.
In 1333 Dietrich had considered dividing the county after his death among his three daughters; however, in the end Kleve came to his brother Johann. Dietrich raised Uedem and Sonsbeck to towns, and in 1334 he founded a convent of the Virgin Mary in the castle of Monterberg near Kalkar, which he moved in 1341 to the town of Kleve. Dietrich died on 7 July 1346, and was buried in the choir of the convent church in Kleve. His widow married Konrad II, Herr von Saffenberg, and had a son Johann who would have progeny.
Dietrich's brother Johann ruled Kleve until his death in 1368. In 1348 he married Mechteld, duchess of Gelre, countess of Zutphen, daughter of Reinald II, Hertog van Gelre, Graaf van Zutphen, and his first wife Sophia Berthout, heiress of Schinnen. The marriage did not result in progeny, though Johann had numerous illegitimate children. With his death the old line of the counts of Kleve died out. Numerous would-be heirs competed to inherit Kleve. Johann's grand-nephew Adolf von der Marck, son of his niece Margarethe, was successful. That family then ruled Kleve until 1609.