Achala was the son of Subala,

Achala was the son of Subala, the Gandhara king.

He was the brother of Shakuni and Gandhari, and thus the brother-in-law of Dhritarashtra and the maternal uncle of Duryodhana.

Achala, along with his brother Vrishaka was killed by Arjuna on the 12th day of war.

Arjuna kills Vrishaka and Achala – the Gandhara princes

Then the two sons of the king of Gandhara viz., the brothers Vrishaka and Achala, those subjugators of hostile towns, began to afflict Arjuna in battle.

Those two heroic bowmen, uniting together, began to deeply pierce Arjuna from the front and from behind with whetted shafts of great impetuosity.

Arjuna then with sharp shafts cut off the steeds and driver and bow and umbrella and standard and car of Vrishaka, the son of Subala, into atoms.

With clouds of arrows and diverse other weapons, Arjuna then once more severely afflicted the Gandhara troops headed by Subala's son.

Then Dhananjaya, filled with rage, despatched to Yama's abode, with his shafts, five hundred heroic Gandharas with upraised weapons.

The mighty-armed hero then, quickly alighting from that car whose steeds had been slain, mounted upon the car of his brother and took up another bow.

Then those two brothers, viz., Vrishaka and Achala, both mounted on the same car, began incessantly to pierce Bibhatsu with showers of arrows.

Indeed, those high-souled princes, those relatives of Dhritarashtra by marriage, viz.,

Vrishaka and Achala, struck Partha very severely, like Vritra or Bala striking Indra of old.

Of unfailing aim, these two princes of Gandhara, themselves unhurt, began once more to strike the son of Pandu, like the two months of summer afflicting the world with sweat-producing rays.

Then Arjuna slew those princes and tigers among men, viz.,

Vrishaka and Achala, staying on one car side by side, with a single arrow.

Then those mighty-armed heroes, with red eyes and looking like lions, those uterine brothers having similar features, together fell down from that car.

Their bodies, dear to friends, falling down upon the earth, lay there, spreading sacred fame all around.