Don is a title which is earned by speaking with Khnum after completing the quest, Stolen Hearts.
This title changes according to the language of the server on which RuneScape is played, as shown below:
||Braço Direito [Name]
- Prior to the Patch Notes of 8 May 2018, this title and the other 3 titles from the Stolen Hearts quest were one of the few titles not available from the Titles interface. On that date they were added to the interface. Previously, these titles could only be set by speaking with Khnum in the Draynor Village jail.