In Blood Omen, Kain found a madman in the north-western corner of Steinchencröe. The lunatic was intently stirring the contents of a pot. Unafraid of the vampire before him, he spoke, happily acknowledging Kain as an outcast of society like himself. He told Kain that other people would speak to him if he knew "how to look".
It was a pun. Kain not only had to seek people, he also had to change his appearance temporarily. He acquired the necessary Disguise form soon afterwards, from a gypsy camp south of Vasserbünde. This made him look like a human peasant.
The madman's identity was never revealed in Blood Omen, or in any official sources this site is aware of. The name appears to originate from the Blood Omen script at Nosgothic Realm; Nosgothic Realm was one of the first Legacy of Kain fan sites, and its popularity seems to have influenced fans to accept 'Irmok' as the madman's name, whether it's actually canon or not.