Hi @reportsbuilder, are you using the Get all deals endpoint? If so, you can use the Properties With History parameter in conjunction with properties parameters to pull historical data for a property. Since won by / lost by are not default properties in HubSpot, you'll need to get the historical data for closedate which does store who closed that particular deal.
Another couple options you might consider are 1) trying to simply pull the owner of the deal (but if multiple people work on the deal at once then that might not work for your purposes) or 2) creating a custom property in your portal that tracks who closed the deal.