He looked very plain and was in his middle years, with lank untrimmed hair. As in the case of Aran'gar, in the choosing of this body for the reincarnation the Dark One (or Moridin) showed his sense of humor because Aginor had a great sense of self importance and he did not like to appear plain and common.
Illian and the Seanchan
When he and Aran'gar (Balthamel) were first resurrected, they were placed under the leadership of Shaidar Haran. Despite infiltrating Rand's Asha'man, Osan'gar still met with the remaining Forsaken and resented the fact the he had to play the part of Dashiva.
After the Battle of Dumai's Wells Dashiva was an Asha'man, chosen by Rand to be one of his bodyguards after being kidnapped by the White Tower Aes Sedai under Elaida do Avriny a'Roihan. He stood guard over Rand when he was meeting with some of the Aiel clan chiefs and when Cadsuane Melaidhrin arrived and insulted Rand.
He was one of Rand's bodyguards when he met with the Sea Folk and made the Bargain. Surprisingly Dashiva seemed concerned when Rand was near death due to being stabbed with the Shadar Logoth dagger, perhaps because the Forsaken had at that point been instructed that Rand was not to be killed. He brought in Damer Flinn to Heal Rand. It was Dashiva's idea for Flinn to start exploring his ability in Healing. He Traveled to Illian with Rand in order to confuse Sammael and try to bring him back to the city of Illian so Rand could finally defeat him.
He went with Rand when Rand tried to deal with the Illian rebels loyal to Lord Brend. He rode with Rand when Rand's forces attacked the invading Seanchan just outside Illian. He tried to warn Rand about saidin not behaving properly around Ebou Dar. On arrival back to Cairhien he accompanied Rand to a meeting with Cadsuane. He used several weaves Rand had never seen before to try to intimidate Cadsuane. Dashiva and several other rogue Asha'man, who turned out to be Darkfriends, attempted to kill Rand and flee, and Rand then followed to try to kill the would-be assassins.
Last seen during the Battle near Shadar Logoth, it is hinted that Osan'gar had been Aginor. Osan'gar tried to use balefire on Rand unseen but he was spotted and attacked by Elza Penfell, a Black Ajah sister who assumed she was killing Dashiva. Osan'gar's body was not seen and the attack not specified as balefire, so it could have been possible for the Dark One to again resurrect his soul into a new body, but he chose not to exercise this option. One of Egwene al'Vere's dreams suggests that he does not return.