Clue: Some Atlantean or Kässbohrer would certainly interest him! (6)
Answer: ANORAK
Explanation: Definition: him
This is clearly mean to be a hidden answer, but it doesn't work – changing the clue to read "AtlanteAN OR **A** Kässbohrer" would fix it. Atlanteans and Kässbohrers are both types of bus, which a bus-spotting anorak might be keen on. Anorak is another of the setter's pseudonyms, as is Busman.