First Appearance: The Doctor Who Magazine #100 (May 1985): "War-Game: Part One"
Number of Appearances: 2
Enemy of: Vegar the Vengeful
Note: loyal advisor to Kaon, who encountered Sixth Doctor
The Doctor and his travelling companion Frobisher first met Achmar when Achmar purchased them as slaves. (The Doctor and Frobisher had been captured and sold as slaves after ordering drinks without having money to cover their tab.)
Achmar was the loyal advisor to Kaon, the Draconian Lord of the Seven Provinces of the planet Actinon. But Achmar himself doesn't appear to have been a "villain" per se. He was simply extremely loyal to his master. He was so loyal, in fact, that he sacrificed himself by leading Kaon's soldiers in an attack on their enemy, Vegar the Vengeful. Achmar died in this attack, which he knew would be a suicide mission. The attack was meant as a distraction so that Kaon could rescue his daughter.
Achmar and Kaon enlisted the Doctor's assistance in their quest. The Doctor could see that Kaon's cause was just. Although Achmar had puchased the Doctor as a slave, Achmar and Kaon actually treated the Doctor fairly well and didn't really treat him like a slave.
Achmar was complicit in leading many of Kaon's soldiers to their deaths, an act one might criticize on moral grounds. But having followers die in order to protect a ruler or a ruler's family is hardly unusual, and was no doubt seen as noble on the planet Actinon.
Suggested links for further research about this character and the character's religious affiliation: