What culture(s) had multiple rulers at one time?

The UK - had Mary II and William III at the same time -

both monarch rather than ususl monarch + consort.

Ancient Rome had the Triumvirates.

Often it doesn't go well - Romulus killed Remus for example.

Any disputed territory technically has multiple rulers.

Rome had multiple rulers during various times in its history, like triumvirate and the Bochho(?) brothers.

Technically the US has multiple rulers, President, Congress, Supreme Court. At times there were more than one Catholic Pope. I'm sure there have to be more but I have narrow history interests and a bad memory.

Rome, the Roman Republic had 2 consuls, who were "elected" officials. The Empire later became fragmented, there were several emperor-claimants and civil wars, and in some cases the father emperor divided the empire up for his sons and made them co-emperors.

Athens had two archons, Sparta had a pair of kings, Rome had consuls.