Nymmurh was granitic in his beliefs that humanity were better than metallic dragons. His thinking was simple: metallic dragons were created by Bahamut to do good and they must not turn away from that, but lesser species could freely choose to be good. He looked to the Harpers and the Order of the Gauntlet as two examples of his theory.
For a long time, Nymmurh protected the noble Waterdeep family of Silmerhelve, to the point that he showed affection to members of the family, as exemplified by Dala Silmerhelve. He apparently chose the Silmerhelve family at random in 1032 DR and over time Nymmurh manipulated the family's members into being kinder, gentler, and slower to act. Sometimes he appeared in front of Silmerhelve members, usually once a generation, as a long-dead ancestor returned from the grave (usually as the mad Lady Saerista Silmerhelve.
He was chosen to be a member of Protanther's council, but he was his most vocal opponent, owing to Nymmurh's strong faith in humanity.