There are many devotees who are eternal servants of the Lord. They are specifically known as nitya-siddha, eternally perfect. Although the nitya-siddhas appear in the material world and seem to be common members of the world, they never forget the Supreme Personality of Godhead in any condition. This is the symptom of a nitya-siddha.

The nitya-siddha never forgets his relationship with the Supreme Personality. By the order of the Supreme Personality of Godhead, the nitya-siddha remains within this material world like an ordinary man, but the only business of the nitya-siddha is to broadcast the glories of the Lord.

From Srila Prabhupada's purport to Cc Madhya 5.113