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Vespasian Kant is mentioned in Liber Tzeentch. He's apparently a friend of Richter Kless and taught him a fair bit of magical theory: enough for Kless to write the sections of the book about the winds of magic. There's also a treatise written by Kant himself, 'Arcane and Divine Magic', in which he argues that the spells of wizards and the prayers or miracles of priests are manifestations of the same power. However, a wizard accomplishes this by directly manipulating the winds, with the aid of long training and will, while a priest does this instinctively, their faith creating an emotional resonance with a deity who then supplies them with power. Kant supports the theory that the gods are themselves Aethyric constructs born of mortal emotion, and suggests that this might account for their relative responsiveness to priests. He suggests that sorcerers of Tzeentch are such powerful wizards because, while they are skilled wizards in the traditional sense, they couple this with abiding faith in a deity who is all too happy to provide them with power. Nonetheless Kant recommends against faith as a path to power for College wizards, and notes that he himself does "not wish to trust the benevolence of a deity whose need for my faith and dedication might far outweight my own need for his or her aid".
Setanta Lobas appears in Liber Nurgle, in a section on beastmen. Lobas doesn't seem very friendly and doesn't like talking, so instead he wrote a report on beastmen and gave it to Kless directly. Despite being an Amber wizard, Lobas seems to be very knowledgeable and scholarly, and his report is quite detailed (twelve pages long, plus three whole-page annotated sketches), so don't believe anyone who tells you that wizards of the Lore of Beasts aren't literate. Lobas knows a lot about beastmen from personal observation: apparently one of his customs is to take the form of a raven and spy on threats to the Empire, so he has a good knowledge of beastman society, rituals practices, and so on. He's pretty knowledgeable about Chaos and the winds too, so it's a good thing he's on the side of order. Still, for all this knowledge, the practical conclusion Lobas draws is that the only solution to beastman presence is to wipe them out: they cannot be negotiated with or redirected.
