In the rich text editor:
@King_Warden
In a comment:
[King_Warden](https://chowlings.com/user/King_Warden)
For Names and Avatars:
In the rich text editor:
%King_Warden
In a comment:
[![King_Warden's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/King_Warden) [King_Warden](https://chowlings.com/user/King_Warden)