Lattice Weston is great. She is immortal and has lived throughout great times in history.
Born in the 1600s in Salem, America as Lattice, she had a great life. She always wished for more time in life. One day, a witch overheard her wishes and granted her immortality. Whoops, bad idea. Upon learning (and her village learning) she couldn't die, she set off on a "Great Walk" and somehow ended up overseas. This is a recurring theme. Lattice has had many aliases and identities throughout life. Her "aging" is very slow and once she "gets too old" it's as if her body resets itself and she turns back into a baby yet her mind is still the same.
Lattice will see and has seen a lot of the world's history. It is presumed she will live right up until the world and time itself ends. Not fun.
She has made an appearance in every series either mentioned or directly involved in some way.