Update Created By (Author) column of SharePoint document using PowerShell

The below script will update the "Created By" site column (also known as document Author) of a SharePoint document or list item.

⚡️ Note - This requires updating the Author and Editor attributes both.

$spWeb = Get-SPWeb -Identity "http://sharepoint_site_url"
$spList = $spWeb.Lists["Shared Documents"]
$spItem = $spList.GetItemById(1)

$SPFieldUserValue = New-Object Microsoft.SharePoint.SPFieldUserValue($SPWeb,1, "LastName, FirstName")

$spItem["Author"] = $SPFieldUserValue
$spItem["Editor"] = $SPFieldUserValue
$spItem.Update()

Make sure you specify the username correctly.