Nothing in the original decans had anything to do with planets, signs, or personality.
They are Egyptian, and they are the oldest layer in this material, older than the zodiac itself. The earliest evidence is a set of tables painted on the inside of Middle Kingdom coffin lids, arranged so that the entries step diagonally down the chart. Each of thirty-six star groups rose just before dawn for a ten-day period, and the sequence of their risings divided the year into thirty-six ten-day weeks. Watched through the night, their successive risings divided the hours of darkness. The decans were a calendar and a clock, and the word simply records the ten.
Each had a name and, in the temple and funerary material, a divine identity. They appear on ceilings, on water clocks, and in the astronomical programme of tombs, and they kept that role for a long time.
What happened next was a merger. When Babylonian zodiacal astrology reached Egypt in the last centuries BCE, the thirty-six decans and the twelve thirty-degree signs turned out to divide the same circle compatibly: three decans to a sign, ten degrees each. The Egyptian star groups were absorbed into the Greek framework as subdivisions of the signs, given planetary rulers by the Chaldean order, and eventually lost their identity as stars entirely. What survives in Western astrology is the arithmetic. The decan is now a ten-degree arc of the ecliptic, and the star group it was named for is not part of the definition.
A separate thread carried the images rather than the arithmetic. The magical tradition, the Picatrix in Arabic and then Latin, and Agrippa after it, preserved a pictorial figure for each decan, a described scene to be engraved on a talisman at the right moment. Those images are transmitted with considerable corruption, they vary between manuscripts, and they do not derive from the planetary rulers. They are a third, largely independent body of decan material, and where a modern source presents decan imagery as ancient Egyptian it is usually reproducing this later magical layer rather than anything from Egypt.