Warcraft II: If I recall the manual, the explanation for Death Knights at that point slightly differed from what's currently on the page: while Gul'dan did use the bodies of fallen human paladins, the Death Knights weren't really undead or corrupted paladins as in future games. The whole thing was an elaborate (and ultimately failed) revenge plot against the current Warchief, who had killed Gul'dan's entire power base to lead the Horde. Gul'dan's remaining acolytes got sacrificed in rituals which resulted in the spirits of the weaker members of Gul'dan's Shadow Council ended up possessing ogres to create the Ogre Mages and those of the strongest reanimated the paladin bodies, letting the Warchief think they were corrupted paladins rather than his enemies brought back under his nose. Fairly sure that got retconned out at some point, but it was the explanation at the time.
Warcraft II: If I recall the manual, the explanation for Death Knights at that point slightly differed from what's currently on the page: while Gul'dan did use the bodies of fallen human paladins, the Death Knights weren't really undead or corrupted paladins as in future games. The whole thing was an elaborate (and ultimately failed) revenge plot against the current Warchief, who had killed Gul'dan's entire power base to lead the Horde. Gul'dan's remaining acolytes got sacrificed in rituals which resulted in the spirits of the weaker members of Gul'dan's Shadow Council ended up possessing ogres to create the Ogre Mages and those of the strongest reanimated the paladin bodies, letting the Warchief think they were corrupted paladins rather than his enemies brought back under his nose. Fairly sure that got retconned out at some point, but it was the explanation at the time.