"Cassian Daniels" is a name that appears in original editions of the first RCN novel, With the Lightnings, due to an error in the editing process.
David Drake originally intended the hero's name to be "Leary Daniels", which was later changed to "Cassian Daniels" in discussions with Jim Baen. Eventually, they decided to use the name "Daniel Leary", but the electronic copy that was sent to the typesetter still had the name "Cassian" in it, and had to be changed in the last minute. During this process, one mention of the old name was overlooked and ended up in the book; the reviewers got advanced copies with the name "Cassian Daniels" as well, thus the name ended up in early editions of the book as well as in many reviews of it.
- David Drake's comment on the name change on david-drake.com