In order to gain immortality, a forgotten race sealed their souls into "heart crystals" which were then placed into Golem bodies. Said race was once again mostly wiped out, due to the fact they could not procreate, until an Ancient Golem King found a way to pull lost souls into new "heart crystals", which could then start their lives as golems. The only problem being that these "lost souls" tend to lose all recollection of what they once were, shatter their crystals over time, and their souls vanish without possibility to return.

Then there's the other drawback that "lost souls" aren't necessarily always from speaking races-- which often results in eccentric personality traits or phobias. (i.e. that golem obsessed with hoarding things, burning things down, and building wings for themselves.) They are also prone to "blacking out" if they don't "rest"-- seems they must sit and meditate after expending energy but can function for four days without rest, if the activity involved isn't demanding. Something about magical regeneration, much as mages can't cast unlimited spells.

When they are crafted, they begin with the mentality vaguely of a "teenager," and pick up skills, language, and interests quickly for a five year period, before their soul "settles", and acquiring new things becomes more difficult-- as difficult as it is for a human adult to learn new skills, at least. No one knows quite how long their lifespan is, though it is estimated to be between 100 and 200 years, with some shattering far later or far earlier in rare instances. The art of forging heart crystals has been with the Royal family for generations and most of the city's golems live within their castle. They're among the last organized golem crafters in the world but certainly not the only ones.

Royal Golems are distinct in that their bodies are specially crafted as they learn their personal identity. Their bodies are only made of Stone and Metal, regardless of the "wood" look some may have-- which was something of a "trendy" look for golems popularized by an artist decades ago. Rumor has it that within the castle resides one of the last Immortal Golems, who is responsible for carving the Royal Golem bodies.

Apparently the only way to truly kill a golem is to shatter their crystal. Transplanting a crystal from one body to another is a dangerous and delicate process-- regardless of how skilled the transplanter is, the crystal is at a constant risk of shattering, as it is exposed to outside magical currents, and the soul longs for freedom. And while most Golems prefer to keep their soul crystal within their chests, that's certainly not the only place to embed it. There are tales of golem heads still talking on long forgotten battlefields or deep beneath the sea, obviously having been driven mad by the isolation-- and rumors of a volcanic cave which screams in a multitude of voices whenever one enters it.

And Royal Golems can't swim. They can't even float.
They simply have not figured out a way to make this possible.