From 11:00PM PDT on Friday, July 1 until 5:00AM PDT on Saturday, July 2, the Shmoop engineering elves will be making tweaks and improvements to the site. That means Shmoop will be unavailable for use during that time. Thanks for your patience!
Dedalus Diggle is one of the Order members who shows up at the Dursleys' house to escort Harry to Number Twelve, Grimmauld Place in the early chapters of Book 5. This is actually his second appearance in the series: Diggle was also the excitable wizard who greeted Harry enthusiastically at the Three Broomsticks in Diagon Alley in Book 1.