WEBI provides you a lot of functions which you can let you perform a wide range of operations ranging from fetching data to doing some complex calculations. You can get the entire list at help.sap.com.
For your requirement you can use from the following functions:
These will not give you directly the name but the id’s which can be used further to get the name.
You will have to utilize the User Attribute Management to get your task done. Create a new variable which you need to populate with the user attribute value basically the name.