The Three Generals were Mevolent's top three generals during the War. Two of the generals, Serpine and Vengeous, are now dead, Lord Vile himself is also technically dead, but only because Skulduggery regained control of himself.
In Mevolent's dimension, Serpine has turned against Mevolent, leaving Vengeous and Vile as his generals.
Serpine was the man who killed Skulduggery Pleasant as well as his wife and child. He possesses a red hand which can inflict immense pain upon a person resulting in death. After the War, Serpine made a truce with the Sanctuary. In the first book, Skulduggery used The Sceptre of the Ancients to kill Serpine after he tried to steal the Book of Names. He was Mevolent's right-hand man.
Known as the most notorious of the Three Generals, Serpine was cunning and insidious, and was also known for his back-up plans, which, according to Skulduggery Pleasant was what made him so dangerous. However, while powerful and feared, he was not the most powerful or feared of the Three Generals, in fact, probably the least powerful and feared. In the third book, we see that Skulduggery is able to defeat Serpine with relative ease in their battle in the caves. However, Serpine has so many little tricks and surprises hidden away, he is able to keep up with very powerful opponents. When he takes control of the Sceptre of the Ancients, he is almost unstoppable.
"You never could fight worth a damn"
After The War ended, Vengeous was imprisoned, but eighty years later was freed by Billy-Ray Sanguine. Vengeous attempted to use the Grotesquery to bring the Faceless Ones back, and even managed to obtain Lord Vile's armour. However, his plot was stopped by Skulduggery and Valkyrie before the Grotesquery could complete its mission, Vengeous was shot by Skulduggery and the Grotesquery was destroyed, both by the combined efforts of Valkyrie Cain, Skulduggery Pleasant, Tanith Low and Mr Bliss.
Lord Vile was the most powerful general. It was once thought that Lord Vile's Necromancy brought Skulduggery back from the dead, but in reality, Vile is nothing but Skulduggery without his conscience. Since only Skulduggery and Auron Tenebrae knew this, it was thought that Lord Vile had been missing, presumed dead, before the first book. Lord Vile returns when Skulduggery's subconscious animates the armour to kill Tesseract and eventually used the armour to become the true Lord Vile again. Vile disappeared during the War after Skulduggery was able to reassert himself.
Alternate DimensionIn the Alternate Dimension, all three Generals as well as Mevolent live on. It is suggested that the dimensions split with Vile's disappearance. In the alternate dimension, Skulduggery never returned and Vile continued to be Mevolent's General, presumably turning the tide of war in favour of Mevolent. Eventually, Nefarian Serpine betrayed Mevolent and turned to the Resistance, even leading it after the event of the death of the alternate dimension's China Sorrows.