Probably not behind (every great man) but more likely than not for most of them. The phrase generally means the woman has made certain sacrafices or delayed the pursuit of her own dreams and aspirations in order to help the man achieve his.
Whether it's actually getting out there for example to help him campaign in order to win an election or taking care of everything else in his life so that he can have a singular focus to pursue his goals. Their willingness to sacrafice at such a high level is what leads many people to consider these women great.
Many of these men alone probably would not have had what it took to reach the pinnacle of their careers.