By observing European huge progresses, the Qajar kings, like other rulers of the region, noticed a new concept named modernization of state. The issue of confrontation of regional powers with each other on the one hand and with European powers, on the other, made the kings to start these reforms from their military forces and army. To operationalize such an enterprise needed expertise and the kings had to employ European military officers individually or in groups. But the paradox was that the aim of European colonizers of sending these military consulting groups was to promote their own strategic and political interests, and colonial rivalries; an issue which was not necessarily in the same direction of designing a coherent, modern and strong army for Iran. This article illustrates the historical trajectory of entering military officers; the officers who entered Iran individually or in formal military groups from European empires such as UK, France, Australia, Italia, Russia and Sweden in order to modernize Iranian military forces. This article also deals with the significant impacts of these individuals and groups and their states on Iran.