In Jain granths, “Achyutendra” (अच्युतेंद्र) is not a human person today, but:

1. Title / position:

Achyutendra = Indra (king of devas) of the Achyut‑vyantar devlok / 12th heaven “Achyut”.

1. As a purva‑bhav (previous birth):

In Ādi Purāṇ and other Jain texts, Achyutendra is one of the previous births of Bhagwan Rishabhdev (Adinath). The famous sequence of his purva‑bhavs includes: Mahābal → Lalitāṅg → Vajrajaṅgh → Bhogabhūmi‑ārya → Śrīdhar‑dev → Suvidhi rājā → Achyutendra (Indra in Achyut heaven) → Vajranābhī Chakravartī → Ahamindra in Sarvārthasiddhi → Rishabhdev Tirthankar.

So, to answer simply:

• Who is Achyutendra “now” in the sense of next birth?

From Jain narrative, that same jīva later takes birth as Chakravarti Vajranābhī, and after further purva‑bhavs ultimately becomes Bhagwan Rishabhdev (Adinath).

For more background on Bhagwan Rishabhdev (Adinath), you can read here and here