The default workflow user in SFDC

The default workflow user is the user who should be assigned as the owner of a workflow action.

- If the user who originally triggered the rule is no longer active. If your organization uses
time-dependent actions in workflow rules, you must designate a default workflow user.

- Salesforce displays this username in the Created By field for tasks, the Sending User field for email,
and the Last Modified By field for field updates.

-  Salesforce does not display this username for outbound messages. If a problem occurs with a pending action, the default workflow user receives an email notification.

To set the default workflow user:

1. Click Your Name ➤ Setup ➤ Create ➤Workflow & Approvals ➤ Settings.

Note: If you click Activate without previously setting the default workflow user and
then click OK in the error dialog, you're sent directly to the Workflow & Approvals
Settings page.

2. Set the Default Workflow User field to any user in your organization. In most
cases, it's best to choose a system administrator.

3. Click Save.

* Workflow is built in business logic