There is no alien race that is 'Nordics'.

The fabricated original claim of encounters with them became popular, and then many other people adopted the name to use with their own claims, both more fabricated ones and true ones.

There are two races visiting Earth who somewhat fit the description of the fictitious race of 'Nordics'.

One is the only alien race of humans that visits Earth, and the other is a race of hybrid people who are half 'The Grays' (not their real name) and half Earth human. [1]