Board Thread:Lore Discussion/@comment-9283242-20130709104327/@comment-6881629-20130709111717

Taker sounds like the basic lowest rank of active assassin (like Murderer in Oblivion) to me, the thing is the Brotherhood didn't really have ranks in Skyrim so i don't know where they really got that info from. Another thing is as organised as they are they are still basicly a cult of Sithis so i don't think every group are always the same except for following the Five Tenets (which Astrid doesn't do in Skyrim).

Found a general lore and history page here on UESP too.