Mar bar Rav Ashi (Hebrew: מר בר רב אשי), (d. 468) was Babylonian rabbi who lived in the 5th century (seventh generation of amoraim).
According to Abraham ibn Daud, he received his personal name (Tavyomi) due to the "good days" (Aramaic: tav=good, yomei=days) which prevailed during his lifetime.
However, this tradition is difficult to understand, since the beginning of his official activity was marked by the bitter religious persecution by Yazdegerd II.
[4] He was not elected director of the Sura Academy until 455 (ד'רט"ו, Hebrew calendar), 28 years after his father's death, when he was chosen under the extraordinary circumstances as described in the Talmud.
His authority in halakhah is shown by a rule (probably of saboraic origin) appearing in Seder Tanna'im veAmora'im, that with two exceptions, decisions are always rendered according to his views.