Pierre Cartier's account of Alexander Grothendieck's life and work includes an interesting reflection from Grothendieck on his time in the IHES seminar:
In a moment of true lucidity, he (Grothendieck) said something like, “I was the only person to have the breath of inspiration, and what I transmitted to those around me wasn’t inspiration, but a job. I had workmen around me, but none of them really had inspiration!”
Many of Grothendieck's collaborators, especially Serre, are considered among the greatest mathematicians of the 20th century. Serre was known for his own significant contributions to algebraic geometry in the 1950s. Did Grothendieck's collaborators really bring so little to the development of modern algebraic geometry? And did Grothendieck ever acknowledge any of his collaborators as his equal?
1) I had begun writing a long answer but I found that analysing the thousand page paranoid rant "Récoltes et Semailles" too depressing.
2) Summing-up: the scandalous calumnies and accusations of plagiarism of Grothendieck toward mathematicians like Deligne, Illusie, Kashiwara, Kawai, Serre and many others would be unforgivable if it weren't for the tragic circumastances of Grothendieck's youth, who had to hide as a child in order not be murdered in Auschwitz like his father.
3) As to the actual question: Grothendieck is undoubtedly one of the greatest mathematicians of all times and his extraordinary creations and prophetic visions attracted some of the best mathematicians on earth to his seminars between 1955 and 1970 (roughly).
These mathematicians profited immensely from Grothendieck's genius, but the converse is also true.
Mike Artin made great contributions to étale cohomology and Demazure, Illusie, Oort, Hartshorne, Manin, Mumford, Murre, Raynaud, Verdier,... had many profound and creative insights which I can't go into for lack of space and above all competence.
Grothendieck apparently couldn't/wouldn't write down his mathematics and the thousands of pages we can read about his oeuvre are the result of the dedication of his volunteer scribes.
In the same vein, the prenotes to Part V of EGA show what EGA would have become without Dieudonné's heroic efforts to clean up the preliminary manuscripts of Grothendieck.
In conclusion, Grothendieck certainly gave a vital impulsion to the renewal of algebraic geometry in the late 50's and 60's, but that field has flowered thanks to the collaborative creativity of incredibly talented young (at the time) mathematicians, none of whom can be dismissed in Grothendieck's scornful way.