SQL server - Find out who is executing the stored procedure from within it

To achieve this you can use SQL functions like

• SUSER_NAME() Function (it returns the login identification name of the user) MSDN article
• CURRENT_USER() (it returns the name of the current user) MSDN article
• USER_NAME() (it returns a database user name from a specified identification number) MSDN article
• ORIGINAL_LOGIN() (it Returns the name of the login that connected to the instance of SQL Server.) MSDN article

Example:

CREATE PROCEDURE
AS 
BEGIN
    DECLARE @executor 
    SELECT @executor = SUSERNAME()
    ...
END

You can read more in this very useful articles:

• Functions That Return User Names and User IDs
• Difference between ORIGINAL_LOGIN and SUSER_NAME

This is a part of my Stackoverflow answer posted 18 Feb 2017