El-Adrel IV
A map of El-Adrel IV.
El-Adrel IV is the fourth planet in the El-Adrel system. In 2368, a Tamarian vessel entered orbit of El-Adrel IV and began sending a signal to the Federation. The USS Enterprise-D arrived three weeks later and attempted to establish communications, but was unable to understand the Tamarians' language.
The creature of El-Adrel IV (2368).
Captain Dathon of the Tamarians then transported himself and Captain Jean-Luc Picard of the Enterprise to the surface of El-Adrel IV, knowing that there was a hostile energy creature there. Dathon hoped that the shared danger would bring Picard to understand him, and he succeeded though at the cost of his own life. The Tamarian vessel had established a scattering field in the planet's ionosphere to prevent the Enterprise from interfering. The Enterprise took down the scattering field in time to rescue Picard from the creature. (TNG: "Darmok")