Stephen Ameyu Martin Mulla, also known as Stephen Ameyu and Stephen Ameyu Martin, (born 10 January 1964) is a South Sudanese prelate of the Catholic Church who has been Archbishop of Juba since 2020, after serving less than a year as Bishop of Torit.
 Pope Francis made him a cardinal on 30 September 2023.
 Stephen Ameyu Martin Mulla was born in Ido in the Diocese of Torit in the Equatoria region of Sudan, now in South Sudan, on 10 January 1964. He attended the minor seminary in Torit from 1978 to 1981 and that in Wau from 1981 to 1983. He then studied briefly at the Saint Paul National Major Seminary, followed by philosophy at the seminary of Bussere (Wau) from 1984 to 1987 and theology in Munuki (Juba) from 1988 to 1991. He was ordained a priest of the Diocese of Torit on 21 April 1991 for the diocese of Torit. He then filled a variety of pastoral assignments for three years.
 From 1993 to 1997 he studied at the Pontifical Urban University, earning a doctorate in dogmatic theology, with a thesis titled "Verso il dialogo religioso e la riconciliazione in Sudan" ("Towards religious dialogue and reconciliation in Sudan"). and from then until 2019 was a lecturer and dean of the Saint Paul National Major Seminary in Juba. He taught evening classes at the Comboni College for Adults and Teachers from 1998 to 2000 and was a lecturer and consultant for the local Sudanese organization for non-violence and democracy (SONAD) from 1999 to 2008. He founded a local humanitarian NGO, the Horiok Community Association and Development (HODA) in 2005 and worked there as a consultant and counsellor for five years. He worked in a similar capacity for women's rights organizations from 2013 to 2016, and then from 2016 to 2019 as assistant vice chancellor for Administration and Finance of the Catholic University of South Sudan and deputy director of the Institute of Applied Research and Community Outreach there.
 On 3 January 2019, Pope Francis appointed him bishop of Torit, a see which had been without a bishop for five years. He received his episcopal consecration on 3 March of that year from Paulino Lukudu Loro, Archbishop of Juba.
 On 12 December 2019, Pope Francis promoted him to archbishop of Juba and he was both installed there on 22 March 2020 and named apostolic administrator of Torit the same day. His appointment as archbishop met with some opposition, possibly tied to ethnic divisions, that included charges of improper influence and unsuitability, which Pope Francis reviewed and nevertheless confirmed the appointment on 6 March. Those who opposed Ameyu's appointment said that they had no objection based on tribal affiliation, though they were Bari and Ameyu is Otuho.
 Since January 2020, he has been vice president of the Catholic Conference of Bishops of Sudan and South Sudan.[citation needed]
 He also served as apostolic administrator of the Diocese of Wau from September 2020 to January 2021.
 He served as host for Pope Francis' visit to South Sudan in February 2023.
 On 9 July 2023, Pope Francis announced he plans to make him a cardinal at a consistory scheduled for 30 September. At that consistory he was made cardinal priest of Santa Gemma Galgani a Monte Sacro.