(Also, see the link 'shikhandi'.)
(In the alternative spelling of this name, the N is pronounced like 'n' in 'turn'.)
Hemavarma was the king of Dashaarna provinces. He gave his daughter in marriage to Drupada's son (in fact , daughter by the time of marriage) Shikhandi. Learning through his daughter that Shikhandi was not a man at all, he rushed to Drupada's place with all his friends and forces to punish Drupada for his cheating act. But , luckily, Shikhandi could get the help of a yaksha named Sthoona or Sthoonakarna and could become a man. Hemavarma did not know that but getting confirmed that Shikhandi was truly a man, he went back happily.
In the war, the Dashaarna king fought on the paandavas' side and was killed by Bhagadaththa. But, we are not sure if it was Hemavarma or his successor.