Cavas is Caeserius Valdo (The Shaper)

CaVa(S?) are the first two letters of each word in his name. Perhaps the S at the end stands for 'Shaper'.

The Shaper has had his memories severely damaged with his fight against the Uber Elder. Eventually the Elder ate all of them up.

That is why his memories are "decaying" (The Elder is an abomination of decay) and unstable. The repeated attacks by Elder have permanently damaged his memory.

In one of his earliest memories is a woman and a child with red hair. Zana has red hair as well.

The Shaper is also an extremely powerful being capable of shaping worlds, it is only fitting that his dreams and memories (maps are referred to as dreams) can drop powerful and unique items. In fact, each memory might not be a memory so much as a map of its own. You can also note that memory nexuses seem to be very high level (mapping level) in the trailer and website, it seems to imply they are similar in nature.

Stop spoiling the very obvious plot!

Next thing you'll tell me the mastermind is piety.