George S. Ledyard
In terms of what is and is not Aikido... On a technical level, Saotome Sensei has been adamant that Aikido has no "style". So, if it has "aiki", on some level it's Aikido. I do think that there is an "attitude" associated with the use of "aiki" principles for waza that he would say distinguishes Aikido from other arts, although not totally even there. Some would say that O-Sensei's talk about Love being fundamental to Budo would be a unique characteristic of Aikido but having worked with the Systema folks and Ushiro Kenji and hearing how they use the term... punching with love, for instance, I would say that it's not unique to O-Sensei.
There is this often-repeated story of O Sensei delivering a 10th dan to a lady dancer when he saw her perform. If it is true, I guess he might have detected, outside of a martial context, a mental/spiritual attitude and perhaps also the use of certain body skills that he judged relevant to his idea of aikido.