Calsidiu is a soldier that is the apparent 'leader' of The Myreque. His two underlings are Veliaf Hurtz and Safalaan Hallow. A further possibility is that Safalaan leads the Meiyerditch-resistance, Veliaf the Myre-resistance, and Calsidiu is their 'leader'. Sani Piliu says in In Search of the Myreque that as far as she knows, he is the 'leader'. Calsidiu is currently missing, and his whereabouts are unknown. Vertida Sefalatis mentions that he may return after Safalaan's disappearance after completing Branches of Darkmeyer.
- The word Calsidiu is an anagram of the word Suicidal, which may be what the resistance ultimately is.