Can someone please tell me who is the person standing in between Hitler and Himmler ?
Thank you.

Who is this ?

Not, as the caption I discovered with this 'photo says, "Hitler receiving the oath"; rather, the consecration of a new SS flag.  The Fuhrer was, like myself, "born and reared" by a devout Roman Catholic Mammy.  Like myself, he effectively renounced Catholicism early in adult life.  However, he was never a man to reject aspects of Catholic worship that might serve his political purposes.  In this case, we are talking about the veneration of relics.  Relics - for anybody who has not come across the concept - are objects connected with a Saint of the Church (or with the Saviour Himself) - that may be venerated by the Faithful.  Like holy statues, the idea is supposed to be that these objects can be used to focus the devotion and meditation of the Faithful; for very many of the same Faithful, the practice may be closer to a form of idolatry.  

I was taught as a child that there were, basically, three classes of relic - primary relics (parts of the saint's body, or his/her blood), secondary relics (objects such as clothing that had touched the saint's body), and tertiary relics (objects that had touched a primary or secondary relic, thus forming some sort of spiritual connection.).  This led to the idea of "consecrating" new Nazi Party flags and banners as relics (don't ask me of which class) by touching them with the "Blood Banner" carried during Hitler's group in the course of the "Beer Hall Putsch" which, supposedly, was stained with the blood of the "November Martyrs" killed during that sorry escapade.  That is what we are seeing in this 'photo.  A much clearer example can be seen in the "banner consecration scene" in Leni Riefenstahl's movie, "Triumph of the Will", in which, in the course of the 1934 Nuremburg Rally, Hitler "consecrates" a large number of SA, SS and NSKK banners by touching them with the "Blutfahne" which is carried, as usual, by its regular bearer and "High Priest", SS officer Jacob Grimminger.  

Other movies from the 1933-'34 period show that Ernst Rohm carried out similar "consecration ceremonies" of SA banners (albeit without the actual Blutfahne).  In Hitler's mind, this can scarcely have suggested to him that Rohm was a man to be relied upon ... JR.

Blutfahne consecration - relic of Catholic youth.

Generalfeldmarschall Wilhelm Keitel is signing the unconditional surrender of the Wehrmacht at the Soviet Headquarters in Berlin-Karlshorst.

Keitel would be hanged on the 16th of October 1946 for his involvement in war crimes, as the chief of the OKW, he would sign orders which were against international law (among them the Nacht-und-Nebel-Erlass).