Morihiro Saito held a 8th dan and was the custodian of the Iwama dojo until his passing went it passed back to the Ueshiba family. The Iwama dojo was where O'Sensei spent a lot of his time and depending on who you talked to the only place where the study of weapons was permitted (most likely because at the Hombu in Tokyo there were many teachers drawing on many weapon lineages and it was confusing for students) Something of a living historian of the art Saito sensei strove to preserve what he learnt from O'Sensei, something that was only recently fully understood when O'Sensei's lost text 'Budo' was discovered. He is famous for exploring the weapons and aikido through the sword stick and body arts books which are now well out of print. Although formally part of the aikikai his school became colloquially known as Iwama Ryu and he began to issue his own certificates in weapons.
With his passing a number of formal Aikido Ryu-ha formed based on Iwama style.