He is Prophet Elias PBUH . Once his name was mentioned Ilias and in another Ayah it was Il-Yassin.
(And indeed, Elias was from among the messenger* When he said to his people, “Will you not fear Allah?* Do you call upon Ba’l and leave the best of creators -* Allah, your Lord and the Lord of your first forefathers?”* And they denied him, so indeed, they will be brought [for punishment]* Except the chosen servants of Allah*And We left for him [favorable mention] among later generations* “Peace upon Il-Yassin.” [As-Saffat 37: 123-130]
إلياس عليه السلام ورد اسمه إول مرة إلياس ، ومرة أخرى باسم إلياسين، وذلك على عادة العرب من إلحاق النون في أسماء كثيرة.
(وَإِنَّ إِلۡيَاسَ لَمِنَ ٱلۡمُرۡسَلِينَ* إِذۡ قَالَ لِقَوۡمِهِۦۤ أَلَا تَتَّقُونَ* أَتَدۡعُونَ بَعۡلاً۬ وَتَذَرُونَ أَحۡسَنَ ٱلۡخَـٰلِقِينَ* ٱللَّهَ رَبَّكُمۡ وَرَبَّ ءَابَآٮِٕكُمُ ٱلۡأَوَّلِينَ* فَكَذَّبُوهُ فَإِنَّہُمۡ لَمُحۡضَرُونَ* إِلَّا عِبَادَ ٱللَّهِ ٱلۡمُخۡلَصِينَ* وَتَرَكۡنَا عَلَيۡهِ فِى ٱلۡأَخِرِينَ* سَلَـٰمٌ عَلَىٰٓ إِلۡ يَاسِينَ)
الصافات 37: 123-130