Algini is one of the more mysterious characters in the series. A member of the Assassins Guild, he is assigned to Bren in the beginning of the primary story in Foreigner, with very little description or background. He is generally described as dour or reserved.
"Algini was a quiet, good man, who could throw a knife with truly uncanny accuracy. Who had gotten, (Tano had hinted,) two very bad assignments from which he had suffered great personal distress and who, Tano had said, had been so quiet within the Guild they’d lost track of him for two years, and dropped him from the rolls as dead until Tano had pointed out he’d been voting consistently and that he could vouch for his identity. They’d been partners for two years on the same assignments and it was the aiji’s request for them as personal security that had pulled up the information that Algini was listed as dead. Algini thought it a joke, quite as funny as Tano did." (Inheritor, Chapter 3)
In later books Algini is mentioned to have been very high ranking in the Assassins Guild, and with some man'chi specifically to the Guildmaster who steps down after the events in the books "Pretender" and "Deliverer."
This would seem to imply that his having been "presumed dead" for two years could have been part of some undercover mission, or possibly even Algini's idea himself, trying to distance himself from certain elements of the Guild. Errors in continuity between this exerpt and later books may also be explained by the fact that everyone lies to Bren as it suits them, especially when it involves the Guild.