Doctor Ja'Dar was a humanoid scientist from the Science Institute on Bilana III who lived during the mid-24th century. He was responsible for the first test of a new method of propulsion, the soliton wave.
In 2368 Ja'Dar initiated the first test of the soliton wave from Bilana III with cooperation from the USS Enterprise-D. Unfortunately the wave did not behave as predicted, becoming dangerously unstable and eventually proving a failed experiment. (TNG: "New Ground")
Ja'Dar was played by actor Richard McGonagle.
He was described in the script as "a middle-aged, humanoid alien who appears totally consumed by his work."
His costume was sold off on the It's A Wrap! sale and auction on eBay. [1]