tatah saptama akutyam
rucer yajño ’bhyajayata
sa yamadyaih sura-ganair
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The seventh incarnation was Yajña, the son of Prajapati Ruci and his wife Akuti. He controlled the period during the change of the Svayambhuva Manu and was assisted by demigods such as His son Yama.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The administrative posts occupied by the demigods for maintaining the regulations of the material world are offered to the highly elevated pious living beings. When there is a scarcity of such pious living beings, the Lord incarnates Himself as Brahma, Prajapati, Indra, etc., and takes up the charge. During the period of Svayambhuva Manu (the present period is of Vaivasvata Manu) there was no suitable living being who could occupy the post of Indra, the King of the Indraloka (heaven) planet. The Lord Himself at that time became Indra. Assisted by His own sons like Yama and other demigods, Lord Yajña ruled the administration of the universal affairs.