Darth Crusher was the Sith General before Darth Revenous. It is unknown who he suceeded. Darth Crusher was created originally as the Sith General to appear in The Mission to Corellia a story by Alex, the creator of Darth Minious and Xander Vos. Darth Crusher turned into Darth Revenous in The Mission to Corellia, as more information was found, but he still appeared as the Sith General prior to Revenous in Destiny Eclipse. There is a brief mention to him in The Mission to Corellia, where he is said to have died during the Jedi Purge, although this is inaccurate as he appears alive and well many years later to kill Jysek Talore in 7 ABY.
It is theorised that he died only a few years later during the Outer Rim Seiges and was replaced by General Revenous. General Revenous was himself replaced by Darth Vexen - widely believed to have been the greatest Sith General of all.