What are customers of IT services who work in the same organization as the service provider known as?

Strategic customers is not a standard ITIL classification for categorizing customers based on their organizational relationship to the service provider.

External customers are those who exist outside the service provider's organization - the direct opposite of what the question describes.

Valued customers is not a defined ITIL term used to categorize customers by their organizational relationship to the service provider.

In ITIL, internal customers are explicitly defined as customers who belong to the same organization as the IT service provider, such as employees or departments receiving IT services from an in-house IT team. This classification distinguishes them from external customers, who are outside the organization and typically governed by formal contracts or underpinning agreements.