Andreas was not always Andreas. Well not until he came to being.
Once upon a time, Andreas was actually a really talented photographer who went by the name of Morgan. Yes, he was a mortal. Anyway, Morgan did the kind of photography that he found most enjoyable and most memorable; photography of people. Believe it or not, he generally did wedding photos, family photos, that kind of stuff. It was enjoyable for him, and he got to help people have memories of the many things in life. To always have memories nearby, was his personal saying. He had good reason why he even did this over anything else. It's because when he lost his parents... he had nothing left to remember them by. Not objects, not photos. Just raw memories of his past.
However, nothing is without its dark times. Morgan got caught in a catastrophic car crash, and he was beyond critically injured. Doctors fought hard... but there was nothing that could save Morgan. He was declared deceased.
But his work... hadn't gone unnoticed. He, in fact, had been noticed by the Titaness of Memory, Mnemosyne. Mnemosyne figured as much that... since he helped people remember things, he deserved to have another chance, even if it meant he'd have to be in her service. So out of that sympathy... Mnemosyne created Andreas, a Memory Spirit, out of the memories that others had with him back when he was Morgan.
True, he was bound in Mnemosyne's service, but now, he had another chance at life. A new life.
Andreas spent the first year or so, figuring out everything and getting used to what he was now. It was only a few days ago, that Mnemosyne decided that Andreas could probably use some time to himself and maybe he should go meet others, so she asked of him to go the Nymph Sanctuary by Camp Half-Blood. He did as he was told, and arrived at the Sanctuary just yesterday.