Why were Hindenburg and Ludendorff a duo when seemingly all the other generals during WWI didn't have a partner?

by tactics14
DuxBelisarius

Hindenburg and Ludendorff were certainly the most famous Duo of the war, but they were by no means the only ones. August von Mackensen had Hans von Seeckt, Ferdinand Foch had Maxime Weygand, Herbert Plumer had Charles Harrington (in fact they were often dubbed 'Plumington'), and Crown Prince Rupprecht of Bavaria had Hermann von Kuhl. There were many commander-chief of staff duos that achieved fame at least among contemporaries, but Hindenburg-Ludendorff feature prominently due to their status after 1916 and their fame as the victors of Tannenberg.