I’m not sure if this is a GQ or an IMHO. Its not really a concrete serious question so I’m putting it here.
Who IS this mysterious Opal? Ender? Could YOU shed some light?
Who is this Wally you keep referring to?
Who is this Jester who keeps popping up? he’s very sexy and I like his style…
Wally is WallyM7, a very respected and beloved member of the SDMB who died some months ago. I’m sure someone will be along in a moment to provide a link to the thread that was started in his honor.
Oh god I’m sorry to hear about that…wow. 
Opal is the snow-loving and prolific OpalCat.
Why does everyone say “Hi Opal!” then?
I’ve been trying to figure this out for a few months myself. My current hypothesis is that Opal is a snow-loving deity, and is placated by frequent greetings.
Of course, I don’t know whether my grasp of theology or meteorology is more appalling…
(Search early and search often!)
Opal hates it when people make lists and then only put two items in the list. So people usually make the third items “Hi Opal!” so as not to have only two. Tacking a “Hi Opal!” onto a list with three or more items is unnecessary. This has been going on for at least two years now, maybe three, so it’s an old joke.
concrete was an annoying troll who kept coming back under various nicknames every time he was banned. He was never banned at Fathom, so you can meet and greet him over there, if you so desire. http://fff.fathom.org/cgi-bin/Ultimate.cgi?action=intro
Here’s a tribute to Wally. http://fathom.org/teemingmillions/wally.adp There are links on that page to many of Wally’s greatest threads. I would especially recommend “Wally tries cybersex!” If you have the desire to do so, search keywords “Wally” and “died” and read a few of the threads that pop up. He was a wonderful and beloved Doper - and human being - who continues to be missed each and every day.
The answer is on this thread
Hi Opal! (WTF?)
I should probably add, being called a putz by Wally was the ultimate and worst insult the SD could bestow upon a poster. The :wally smilie is in remembrance of him.