Information is available in Haik Patapan's Arti Etovpia ev Hay kaghoute, published in Venice in 1930.
Hrant Minassian was an uncle of Matig Kevorkoff. He had been associated to him for his business for almost 50 years, until 1924. At this date, Kevorkoff started to work alone.
In 1930, Patapan's book cited the "Maison Minassian", together with "Maison Kevorkoff", among the most prominent Armenian trade-houses in Ethiopia. The "Maison Minassian" had its central office in Dire Dawa, but held also shops in Harar and Addis Ababa.
As a trader Matig Kevorkoff was, as far as I (Boris Adjemian) know, the main one in Armenian Community and a very famous one in Ethiopia. Born in Iskiudar (near Constantinople) in 1867, he was well educated in the Armenian college Hagop Kurken from Constantinople. Arrived in Djibouti in 1896, after a short stay in Egypt, he created his trade company. The company grew and expanded towards Ethiopia (Dire Dawa, Harar and, of course, Addis Ababa). Kevorkoff imported cotton, silk, beverages, olive oil, soap, perfumes, iron and building materials. But Matig Kevorkoff was especially renowned for his monopoly over tobacco trade in the whole Ethiopia. This monopoly was the base of his fortune. He also became one of the first Administrators of the new Bank of Ethiopia. He was decorated many time by the Ethiopian government and was elected in 1927 president of the Armenian Community in Ethiopia.
It is important to say that Matig Kevorkoff was a French citizen (probably naturalised in Djibouti). He was famous at the French Legacy in Ethiopia. In 1920, Avedis Aharonian, in accordance with French authorities, asked Kevorkoff to be the "Représentant diplomatique de la République arménienne" in Ethiopia (like an acting ambassador of the Republic of Armenia born after First World War). The year before, in 1919, he had given 1,000 English pounds, together with other Ethio-Armenians in order to help the young Armenian Republic to buy an airplane.