Hello Olga_L,
David Bowie struggled with his identity and expressed himself through his songs, often creating characters to perform them.
In this song he is referring to himself as the ' man who sold the world.'
Quoting some lyrics to show the reference:
*"We passed upon the stair"
is a figurative representation of a crossroads in Bowie's life, where Ziggy Stardust catches a glimpse of his former self, (being David Bowie) which he thought had died a long time ago. Then he (the old David Bowie) says:
* "Oh no, not me. I never lost control." This indicates that Bowie never really lost sight of who he was, but he Sold The World (made them believe) that he had become Ziggy, and he thought it was funny (I laughed and shook his hand). He goes on to state,
* "For years and years I roamed," which could refer to touring for musical performances "Gaze a gazely stare at all the millions here" are the fans at concerts.
However there has been many different interpretations of those lyrics.
The text is that kind that is open to various interpretations from different point of views.