Serge Gainbourg was a pigmallion (sp?) first and foremost.
He launched the career of several young women in France. Without him Jane would've probably fallen into oblivion.
He was extremely talented and is considerated like one of the most talented composer and singer of the recent past in France. He dated the most beautiful women of his lifetime (Bardot, Birkin...) so I guess that yes he was extremely charming.