@tuitendung Both the values are same, the difference lies between the data type of both the fields. Created_by fields captures the string value of user name. Whereas Opened_by is a reference field which captures the sys_id and shows the name field as display field from sys_user table.

In the first row of the screenshot you shared, created_by has abel.tuter populated which is a string value of user_name of Abel Tuter. On other hand Opened_by contains Abel Tuter which is a reference field and shows Name of the User from sys_user table.

Hope this helps.