Why 'Salesforce Administrator' Appears in Last Modified By After Custom Field Deletion

Cause

The 'Salesforce Administrator' user that appears in the Last Modified By field is not a real person. It is a system-level user that Salesforce uses when an automated background process modifies metadata, such as page layouts, record types, or custom objects.

How the Physical Delete Process Works

When a Salesforce administrator deletes a custom field, the field is not immediately removed from the system. Instead, it is marked as "soft deleted" and remains in Salesforce for a minimum of 30 days. After this period, Salesforce runs a "Physical Delete" (also called a "hard delete") process to permanently remove the field from the database.
As part of this process, Salesforce removes all references to the deleted custom field from any associated page layouts, record types, and custom objects. Because these items are technically modified during this cleanup, Salesforce records the modification as being made by 'Salesforce Administrator'.

What You Can Expect

This is expected Salesforce behavior and does not indicate that any unauthorized changes were made. No action is required. If you notice 'Salesforce Administrator' in the Last Modified By field, it is a sign that a soft-deleted custom field was recently hard-deleted from your org.