Malak-ul-Maut is the Angel of Death who takes people's souls at death by the will of Allah. The Angel of Death is frequently referred to as Izrael; however, the authentic sources refer to him as Malak-ul-Maut only.
Say, "The angel of death will take you who has been entrusted with you. Then to your Lord you will be returned." (Quran Surah 32:11)
The angels are not partners, associates, or rivals with Allah, nor are they His children; but one must still respect and love them. Allah says: "And they say: ‘The Most Beneficent (Allah) has begotten a child [from the angels].’ Far removed is He from every imperfection! They (the angels) are but honored slaves. They speak not until He has spoken, and [then] they act on His Command." (Quran Surah 21:26-27)
They spend their time worshipping and obeying Allah, glorifying Him and praising Him. Allah says: "They (i.e. the angels) glorify His praises night and day, (and) without slackening (to do so)." (Quran Surah 21:20) 
Narrated Abu Huraira(R): The angel of death was sent to Moses and when he went to him, Moses slapped him severely, spoiling one of his eyes. The angel went back to his Lord, and said, "You sent me to a slave who does not want to die." Allah restored his eye and said, "Go back and tell him (i.e. Moses) to place his hand over the back of an ox, for he will be allowed to live for a number of years equal to the number of hairs coming under his hand." (So the angel came to him and told him the same). Then Moses asked, "O my Lord! What will be then?" He said, "Death will be then." He said, "(Let it be) now." He asked Allah that He bring him near the Sacred Land at a distance of a stone's throw. Allah's Messenger (ﷺ) (p.b.u.h) said, "Were I there I would show you the grave of Moses by the way near the red sand hill." Sahih al-Bukhari 1339 (Vol. 2, Book 23, Hadith 423)
A Muslim must believe specifically in all the angels named and/or described in the Qur'an and the ahadith: