Sokaku Takeda taught Morihei Ueshiba Daito Ryu Aiki-jitsu.
It was Ueshiba's personal expression of this martial art which became Aikido. Both men agreed that Ueshiba's art was so different than Daito Ryu, it should be given a new name.
Today, there are many people practicing Aiki-jitsu. Some also practice Aikido. Which brings about this question:
Should a person practice Aiki-jitsu to try and gain some insight about Aikido? Or should a person just practice Aikido?