Leads Created from the User Interface Automatically Uses the Assignment Set from Sales Rules and Territories

By default when leads are created from the user interface, the user creating the lead is automatically set as the Primary Sales Rep of that record. Do note that an exemption is made when the user creating the lead record does not have a Sales Role. Automatically if the person creating the lead does not have a Sales Role, the Sales Rep assigned to that record is the Sales Rep that is set from the company's Sales Rules and Territories.