Step 1: Identify the key parties involved.
The question is about protecting the interests of 'depositors', who place fixed deposits with a company.
Step 2: Analyze the roles of the options provided.
Debenture trustees are appointed to protect the interests of debenture holders.
Deposit trustees are appointed specifically to safeguard the interests of individuals who have deposited money with the company. They act as a liaison between the company and the depositors.
A Credit Rating Agency assesses the financial health and creditworthiness of a company but does not directly protect depositors' interests.
Step 3: Match the role to the requirement.
The correct entity appointed to protect depositors is the Deposit trustee.