The leader of Asuras, also known as Asurapati. The only one alive is Raja Bali who is now under protection of Shriman Narayana in the form of Vamana avatar.
If he is in some other place and not ruling asuras, then who is the current Asurapati?
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As per Śrīmad-Bhāgavatam (Bhāgavata Purāṇa) » 8.22, Bali Mahārāja is still the ruler of Asuras (mainly Daityas):
SB 8.22.31 — The Lord continued: Because of his great tolerance, I have given him a place not obtainable even by the demigods. He will become King of the heavenly planets during the period of the Manu known as Sāvarṇi.
SB 8.22.32 — Until Bali Mahārāja achieves the position of King of heaven, he shall live on the planet Sutala, which was made by Viśvakarmā according to My order. Because it is especially protected by Me, it is free from mental and bodily miseries, fatigue, dizziness, defeat and all other disturbances. Bali Mahārāja, you may now go live there peacefully.
SB 8.22.33 — O Bali Mahārāja [Indrasena], now you may go to the planet Sutala, which is desired even by the demigods. Live there peacefully, surrounded by your friends and relatives. All good fortune unto you.
SB 8.22.34 — On the planet Sutala, not even the predominating deities of other planets, what to speak of ordinary people, will be able to conquer you. As far as the demons are concerned, if they transgress your rule, My disc will kill them.
Rulers of other sub groups of Asuras are mentioned in Śrīmad-Bhāgavatam (Bhāgavata Purāṇa) » 5.24 with their Lokas:
In Atala: Bala Dānava
In Talātala: Maya Dānava
In Rasātala: Many Dānavas and Daityas groups: Paṇis, Nivāta-kavacas, Kāleyas and Hiraṇya-puravāsīs