The Many Names of the Founder of Islam

Abu Musa Ash'ari reported that Allah's Messenger (ﷺ) mentioned many names of his and said:

I am Muhammad, Ahmad. Muqaffi (the last in succession), Hashir, the Prophet of repentance, and the Prophet of Mercy.

https://sunnah.com/muslim:2355

Narrated Jubair bin Mut`im:

Allah's Messenger (ﷺ) said, "I have five names: I am Muhammad and Ahmad; I am Al-Mahi through whom Allah will eliminate infidelity; I am Al-Hashir who will be the first to be resurrected, the people being resurrected there after; and I am also Al-`Aqib (i.e. There will be no prophet after me).

https://sunnah.com/bukhari:3532

Jubair b. Mut'im reported on the authority of his father that he heard Allah's Messenger (ﷺ) as saying:

I am Muhammad and I am Ahmad, and I am al-Mahi (the obliterator) by whom unbelief would be obliterated, and I am Hashir (the gatherer) at whose feet mankind will be gathered, and I am 'Aqib (the last to come) after whom there will be no Prophet.

https://sunnah.com/muslim:2354a

Jubair b. Mut'im reported on the authority of his father that he heard Allah's Messenger (ﷺ) as saying:

I have many names: I am Muhammad, I am Ahmad, I am al-Mahi through whom Allah obliterates unbelief, and I am Hashir (the gatherer) at whose feet people will be gathered, and I am 'Aqib (after whom there would be none), and Allah has named him as compassionate and merciful.

https://sunnah.com/muslim:2354b

If he has many names, including Muhammad, then is Muhammad actually his birth name? All the others are self-assumed titles. If he is Al-Hashir, The Gatherer, is he actually Allah? He is supposedly called Al-Mahi, through whom Allah would remove kufr. But in another hadith we read that Isa would come and break the cross.

It is narrated on the authority of Abu Huraira that the Messenger or Allah (ﷺ) observed:

I swear by Allah that the son of Mary will certainly descend as a just judge and he would definitely break the cross, and kill swine and abolish Jizya and would leave the young she-camel and no one would endeavour to (collect Zakat on it). Spite, mutual hatred and jealousy against one another will certainly disappear and when he summons people to accept wealth, not even one would do so.

https://sunnah.com/muslim/1/296

So wouldn't Isa be Al-Mahi?

In the Quran he is called kind and merciful.

S 9:128 A messenger has come to you from yourselves. Dear to him is what you have suffered. Greedy upon you. To the believers is he kind, merciful.

But Allah is called kind and merciful. https://www.answering-islam.org/authors/rogers/most_kind.html

Muslims have given him many names, some of which are also applied to Allah. A list: http://www.ezsoftech.com/islamic/infallible1f.asp