SharePoint portals are tightly integrated with Active Directory and since SharePoint has a additional Database to maintain user profiling, However many times user alias names are shown inconsistent on welcome.ascx section For some it's show :
• first name , last name
• last name, first name
This means AD-Profile Synchronization is not enabled or not happening for some reasons.
Manually run following SharePoint PowerShell Command which synchronizes AD Accounts.
Get-SPUser –Web http://SharePointServer | Set-SPUser –SyncFromAD
Execute command for each Site collection to reflect these changes.