Copper Golem is a built mob rather than a spawned one, and it exists to move items for you. Place a block of copper in any oxidation or waxed state and set a carved pumpkin or jack o'lantern on top of it last; the copper block becomes a copper chest and the Copper Golem steps out beside it at the same oxidation stage.
Its job runs one way: it lifts items out of copper chests and carries them into nearby wooden or trapped chests, looking for one that already holds that kind of item. That habit is the backbone of a copper golem sorting system — seed each destination chest with a sample of what belongs in it and the golem empties the copper chest into them unattended. It carries up to 16 of one item per trip, opens any door that is not iron, and ignores ender chests, chest minecarts and dropped items.
Its search box is wide and shallow — roughly 65 blocks across and 17 tall around itself — so a sorting room that spreads out works and one stacked over floors does not. A Copper Golem cannot be tamed or commanded, only placed well: build it where the chests are, with a walkable route between them.
Copper ages, and so does the golem. Left unwaxed it works through the four copper stages and eventually stops moving altogether, petrifying into a copper golem statue that keeps the pose it froze in and can be cycled through the others by interacting with it. Honeycomb waxes a Copper Golem and stops that clock; an axe scrapes oxidation back off, and using one on a statue reanimates it, so petrification is a pause, not a loss. A golem gifted a poppy by an iron golem holds onto it, and shears are what take it back.