© CC0 1.0Alexander and his queen at table, and again in the foreground with a feather in his throat after being poisoned, 323 BC.
Family Ties
Ptolemy I Soter was born in 367 BC. He was perhaps the half-brother of Alexander and son of Philip II of Macedon with the beautiful Arsinoe. To avoid problems, Philip may have arranged the marriage of Arsinoe with a Macedonian nobleman named Lagus.
Regardless of a certain familial link, Philip treated Ptolemy as his own son. He took him to the capital at a young age and gave him as good of an education as he offered Alexander. Ptolemy was also sent to the school of Aristotle, where he was considered a talented student. It is unlikely that Philip would have invested so much attention and invited him to live in his palace, if Ptolemy had not been his child.
Everything in Ptolemy's life suggested that he would be a very successful person, but, at least for a time, he had to stay in the shadow of Alexander.
Ptolemy was considered a great warrior and very well-educated in the art of fighting. He soon became not only the closest friend of Alexander, but also his personal guard called ''somatophylakes''. He was a few years older than Alexander, tall and fit.
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this is not what I have read. According to other sources Ptolemy was actually not that close to Alexander, from a minor nobility and pure chance or rather very strong stomach, (most other more notable warriors died from various diseases during Alexander's invasions) elevated him rather quickly to the position of a general and later to one of the people to divide the kingdom. There were other generals that took precedence to him and this is why after Alexander's death, they took the more appetising parts of Greece. Egypt was not considered as prestigious, so it was given to Ptolemy.