Akara is the "High Priestess of the Sisterhood of the Sightless Eye". What exactly that title means is unclear, but she seems to be a spiritual leader of sorts.
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Background
Akara is the presumed spiritual leader of the Order of the Sightless eye, which may make her the order's primary leader.
Diablo II NPC
Akara was one of the leaders of the rogue camp in Act I of Diablo II, along with Kashya. She gave out 2 quests, and had interesting dialogue for some of the others. She also healed players and sold staves, wands, scepters, scrolls and tomes, and mana and health potions.
For more information about the Diablo II NPC Akara, see: Akara in the Diablo II wiki.
In Diablo III
Akara's status at the time of Diablo III is unknown. At the end of Diablo II she was last seen working to rebuild the sisterhood after Andariel's defeat. Her age was unknown, though she was presented as old. It seems likely she is dead, although a return in Diablo III is entirely possible.