Hi Maxim,
On the entity comment check the box Store owner, (there is no need to have an attribute to store the name).
To display the name associated to that comment the path should be
System.owner/Administration.Account/Administration.Account.FullName
"This is an association to the system entity ‘User’ that (initially) stores a reference to the user that created the object. This association is automatically set by the server upon creating an object."
Some documentation about the above:
https://docs.mendix.com/refguide/entities/#343-store-owner
https://forum.mendix.com/link/questions/96608
I hope will help :)