Step 1: Understanding the Question
This question asks to identify the profession or role of the character Mr. Herriot, who is the narrator of the story "A Triumph of Surgery".
Step 2: Recalling the Story Details
In the story, Mr. James Herriot is a veterinary surgeon. He is approached by Mrs. Pumphrey about her overweight dog, Tricki. He diagnoses the dog's problem and takes it to his surgery (hospital) for treatment.
Step 3: Detailed Explanation
As a veterinary surgeon, Mr. Herriot is a doctor for animals.
(A) A compounder assists a doctor, which is not his role.
(C) While he might live near Mrs. Pumphrey, his primary role in the story is professional, not as a neighbour.
(D) Although he helps Tricki recover, his profession is a veterinarian, not simply a dog trainer.
Therefore, 'A doctor' is the most accurate description of his profession.
Step 4: Final Answer
Mr. Herriot was a veterinary doctor.