What is sap_wfrt?

The SAP standard workflow is used for FI document parking and release. First make sure you have created system user SAP_WFRT. I am just not sure where this 'SAP_WFRT' user is coming from and it's clear that the RFC destination uses the 'WF-BATCH' user. The following error occurring, when trying re-customize workflow in SWU3 transaction: System user 'SAP_WFRT' does not exist. The system user SAP_WFRT with authorization SAP_ALL and role Z_RFC_ALL ( includes authorization RFCACL) must be available within the client before you. Custom logic implementation fails for SAP_WFRT user due to authorization issues.