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