MMH5.5 - Heroes of Might and Magic 5.5

Where? In custom game he is Death Knight.
Does he appear in campaign and if so what hero class he is ? In campaign heroes should be a class similar to what they are in campaign, if they are not this is an oversight from our side.

Please also mention a mission name if relevant.

I do not remember him in campaingns but in the original game Kaspar are a Necromancer with specialisation is Embalmer "The First Aid Tent will heal 5 more hit points per hero level. The damage in case of PlagueTent ability is also increased." and his bio "Kaspar was a great doctor and healer who was able to cure even the most terrible wounds. Delving deeper and deeper into the secrets of life and death, Kaspar made a particularly risky experiment that went wrong... and brought him to the realm of the dead. Though he now leads an undead army, his knowledge of anatomy and the treating of wounds remains unparalleled."!

Therefore in my humble opinion this is clearly not a Death Knight but like a Necromancer!