My vote goes to Neitzsche.
Kant. He’s so deep you can’t see the bottom.
Or the top.
Or the middle.
i find Kierkegaard even deeper in some ways
but nobody exposed the depths of human nature like Nietzsche did - cept perhaps Dostoevsky, to whom I’m already willing to give the benefit of the doubt in this discussion, that is, despite me having just recently stumbled upon his work, and being only two-thirds through my first of his works (Notes from Underground).
Like N, D is fucking brutal.
Oh, and Plato more than deserves a mention here - centuries have passed, and yet the man continues to occupy heights few have touched since.
werklempter by a fathom
-Imp
Good call.
Yeah, I’d call Plato insightful, but not deep. Socretes, on the other hand, was a deep dude.
Tu Weiming
Was he buried before Thales? …just sayin’. 
Edit: Ok. Still living. Guess that answers the question. Unless life is deeper than death, of course. 
He’s one of the most recent steps on a path that predates Thales, if that is any consolation to you. Knowing what to do with an inherited tradition is part of depth, after all.
As for his status . . . errr, I guess he is still alive. But barely. Dude is already filling out paperwork in the celestial bureaucracy, if that helps raise his street cred.
Gilles Deleuze
Nietzsche is a close second
ever consider that it just might be that guy who wrote Ecclesiates - Qoheleth was his name. have you ever really read it? it is just so philosophically sound and deep, so very much room for thought to ponder in it about one’s life and about Life. perhaps he wasn’t considered a philosopher in his time, but trust me, he was a philosopher. read Ecclesiastes.
it occurred to me that it may be possible that much thought that comes from philosophy and philosophers may perhaps have been borrowed from his thoughts. there is after all a wealth of information, insight, wisdom and truth in there to ponder.
Davy Jones
Gotta agree with faust here, even schopenhauer was amazed by Kant.
The old testament doesn’t have universal concepts, this was given to us by the Greeks. OT is very existential, but by no means would it suffice to say that “much thought” comes from it in philosophy. The Greeks went into detached contemplation and dialectics, essences, platonic world, while the OT remained firmly rooted in man and man and his relation to god–the I and the Thou. The Hebrew of the OT does not even have a word for nature. They have garden… etc… but not nature, not a universal concept. Therein lies one of the great distinctions that have formulated our history, the binary between the two great traditions that have taken on so much weight in the West, Hebraic man and Hellenic man.
As far as the deepest goes… depends on what field of philosophy we’re digging through.
Nobody knows because He or she or it never spoke…
Sir, with that quote, you just may be the deepest (at least second to he who doth not speak, of course 
).
It need not be universal in order to be philosophy, nor for classical greek philosophy to have borrowed from it.
I don’t think wisdom implies or necessitates silence.
Nietzsche, and I think it’s because his philosophy is much more personal and more useful than other philosophers. The ‘will to truth’ corrupted philosophy and blinded philosophers. The philosopher began to serve philosophy, instead of the other way around. The last great philosopher before Nietzsche is Heraclitus, I think.
[size=85]Life no argument.— We have arranged for ourselves a world in which we can live—by positing bodies, lines, planes, causes and effects, motion and rest, form and content; without these articles of faith nobody now could endure life. But that does not prove them. Life is no argument. The conditions of life might include error.[/size]
no but depth implies that the deepest part of the philosopher in question would be incomprehensible, thus they would essentially be silent in the matter.