⚠ Elisha ben Abuya — Acher, "Other"אלישע בן אבויה

One of the four who entered the orchard, and the one the tradition could not decide what to do with. He "cut down the saplings" — became a heretic — and thereafter the Talmud mostly declines to use his name, calling him אחר, Acher, Other.

⭐ What ruined him is a sentence, and the Gemara says so before it tells you anything else: "Acher cut down the saplings. Of him the verse states: do not let your mouth bring your flesh into guilt" (Ecclesiastes 5:5). See two-powers. This app puts him in the same room as Akiva's marble on purpose — two catastrophes in one tractate, and the Gemara hangs both of them on a verse about the mouth.

He does not stop being a teacher. Rabbi Meir goes on learning from him after the break, and the Gemara records their exchanges without apology.

⭐⭐ And the tradition will not leave him where it put him. At his death the Heavenly Court would neither judge him (he had occupied himself with Torah) nor admit him (he had sinned) — so Rabbi Meir undertook to have him judged, that he might then be brought in, and smoke rose from his grave. Then Rabbi Yoḥanan: "Was this a mighty deed on Rabbi Meir's part, to burn his teacher? Can it be that there was one Sage among us who left the path and we cannot save him? If we hold him by the hand, who will remove him from our protection; who?" — and when Rabbi Yoḥanan died the smoke ceased (Chagigah 15b).

⚠ Kept unresolved, because the page is. It also records that he heard a Divine Voice call every rebellious child home except him, concluded he had nothing left to lose, and spent what was left. Two of his students argue over his grave for a generation. The tradition neither approves of the fall nor finally abandons him.