Tobi could infact be a tired and irritated at the world Rikdou Senin Himself? HE maybe lost a major part of his powers fighting the jyubbi. It is strong possiblity as Minato insisted that kyubbi's chakra will be required to defeat him and I do not think 4th would be fooled tht he was madara that easily. So only a strong past ninja with a history with the kyubi makes sense. that leaves Rikdou and probably his sons!