Astrogha
Astrogha is the favored servant/pet of Diablo always hiding in the shadows scheming. Its first appearance in the Sanctuary was during the Sin War when she was summoned by Lucion to assist against Lilith.
Astrogha always have little spider spies to gather information about everything that's of interest. It feeds on humans which Lucion uses to his advantage. It doesn't help lucion willingly, however it always stays loyal to its master Diablo. Astrogha have even plotted to overthrow Lucions rule as Primus but after careful consideration it backed off since it doubted the backing of Diablo when Mephisto's wrath would show it self after Lucsion's "disappearance". After Lucsion was reduced to mere ashes Astrogha plotted to take over the role as Primus once again, but when he reappeared (Lilith disguise]] it backed off. After realizing this Astrogha started to scheme against Lilith and even taking the appearance of Primus for a short while. However this ended with a showdown between it and Lilith which Lilith won. After that Astrogah was back in the shadows plotting.
Ages after The Sin War astrogah was reincarnated in the Moon of the Spider, where it was imprisoned in a orb. This orb was the work of the Vizjerei. It was released by a noble from Westmarch with the name Aldric Jitan. Astrogha led its children to attack the capital of Westmarch and nearly succeeded. Without the intervention by Zayl and Salene Astrogha would have succeeded, but they managed to seal it back to the orb (moon).