(defun explode (string1)
(let* ((character (string (char string1 0)))
(new-string (subseq string1 1))
(new-length (length new-string)))
(cond ((eql new-length 1) (list character new-string))
(t (cons character (explode new-string))))))
...which leads to....
; SLIME: The Superior Lisp Interaction Mode for Emacs
CL-USER> (explode "This a string")
("T" "h" "i" "s" " " "a" " " "s" "t" "r" "i" "n" "g")
CL-USER>
mwg