Muhammad ibn Hasan al-Mahdī (محمد بن الحسن المهدي), also known as Imam Zaman (Persian: امام زمان), is believed by Twelver Shī‘a Muslims to be the Mahdī, an eschatological redeemer of Islam and ultimate savior of humankind and the final Imām of the Twelve Imams who will emerge with Isa (Jesus Christ) in order to fulfill their mission of bringing peace and justice to the world. Twelver Shī‘a believe that al-Mahdī was born in 869 (15 Sha‘bān 255 AH) and assumed Imamate at 5 years of age following the killing of his father Hasan al-Askari.
Dajjal is the last leader of falsehood, will come before the reappearance of Imam Al-Mahdi (AS). He will be killed by the last leader of righteous, Imam Al-Mahdi (A.S.). Dajjal is one of the definite signs of the reappearance of Imam Al Mahdi (A.S.). Dajjal will lead an army of the enemies of Ahlulbayt and fight against Imam Al-Mahdi (A.S.) and he will be defeated. (Al Amali by Al Toosi, Page 459). It is mentioned in Kamaal Ad-Din Page 336 from Imam Jafar As-Sadiq (A.S.) that Imam Al-Mahdi (A.S.) will kill Dajjal. Unfortunately, we read narrations in some Sunni books, which are taken from Non-Muslims and it go against the Truth. For example, the narration in Sahih Muslim which is called Hadeeth Al-Jassasa Volume 8 Page 204 & Hadeeth in Sahih Al Bukhari about Ibn Sayyad who is according to the narration of Bukhari the Dajjal. Ibn Hajar Al-Asqalani in Fath Al-Bari Volume 13 Page 276 confirmed his opinion that Dajjal is still alive. We don’t have in our authentic narrations the exact date when Dajjal was born and in fact we don't need it, but we only need to know that Dajjal is a devil satanic leader and he will lead his followers to the hellfire, and he will fight against Imam Al-Mahdi (A.S.) and he will be killed by Him. (Al Amali by Al-Toosi Page 527, Al- Bihar Volume 76 Page 74, Al-Waafi Volume 26 Page 186).
Yes, it is mentioned in many narrations that Imam al-Mahdi (AS) will martyred and Imam Husain (AS) will pray his Namaz e Janaza. (Biharul Anwar , volume 53, page 103 and Al-Kafi 8:250)
There is a very beneficial video series about the topic here:
The sincere believers will obey the orders of Imam Al-Mahdi (AS) in every matter in their life. He will not order all the believers to fight. His aim is not merely fighting but only against the enemies of human beings who are the tyrants. He will clean the whole earth from tyranny and injustice and fill the whole earth with justice and fairness.
He will never ask people to do any thing which they do not know, so, if you have no experience in fighting, you will not be asked to fight, unless you go through suitable training which makes you able to fight. That also only fighting was required in your area, which is not confirmed in every area. We need to prepare ourselves to obey the orders of our Imam (AS) but we can never know now whether he will order us to fight against the enemies of human beings or to build our societies and serve people.
Short answer: Yes and no.
"Al-Qa'im" means "the one who rises up" [for instance, against injustice]. It is primarily used for the Mahdi, but it can also be used for all the Imams.
The literal meaning of the word "al-Qa'im" does not specifically relate to one's name being unused; it comes from the word meaning "to rise" or "to stand".
However, titles for the Mahdi (including al-Mahdi and al-Qa'im) have been used instead of his personal name (which is the same as that of the Prophet (S)) because there are narrations saying that you should not refer to the Mahdi by name. So, in that sense, the Qa'im will arise when people are not referring to him by name; rather, they are referring to him as the Mahdi or the Qa'im.
[For instance, see https://www.al-islam.org/kamaaluddin-wa-tamaamun-nima-vol-2-shaykh-saduq... ]
It is also mentioned in a couple narrations that the Mahdi is called "al-Qa'im" because his occultation will last for a very long time. Therefore, when he reappears, people will have forgotten him so much that it will be as if he is rising up as a new creation. [Similar to how, on the qiyamah or Resurrection, people will rise up anew after being dead.]
[For instance, Bihar al-Anwar, vol. 51, p. 30 - سمي القائم عليه السلام قائما لأنه يقوم بعد موته ذكره. - "he is called the Qa'im because he will arise after his remembrance has perished".]
This is similar to narrations which say that the Mahdi will reappear in a time when faith is at an all-time low. So, in this sense, he may not be commonly spoken about before his reappearance.
So, you can say that both:
(a) The Mahdi is called "al-Qa'im" because he will lead an uprising [this is explained, for instance, by Imam al-Sadiq], and
(b) The Mahdi is called "al-Qa'im" beacuse he will arise at a time when his name has been forgotten, and therefore will be rising up anew.
The first view (that he is called al-Qa'im because he will lead an uprising) is the more commonly understood meaning, but both views are supported by narrations, and one can say that he is called al-Qai'm for both reasons.
Hope that helps!
Some narrations about the raj'ah specifically mention the return of people from ancient times. Of course, not all narrations about the raj'ah are correct, and maybe those are not correct, but, at least, from what we have, it seems that the raj'ah will include people from all times and not only the time after certain Imams.
However, according to narrations, not all people return in the raj'ah. Only those who have the highest level of faith and highest level of depravity will be brought back to life.
Imam Al-Mahdi (AS) will not fight but only against those enemies who insist on fighting him. Non Muslims will never be forced to become Muslims. The Prophet Muhammad (SAWA) and Imam Ali (AS) never forced any non Muslim to become a Muslim. Imam Al-Mahdi (AS) will be applying Islamic rules in the same prophetic way.
1. Being pious in every act we do and every word we say.
2. Remembering the fact that our Imam Al-Mahdi (AS) is alive and he is informed about our acts and deeds and trying to always please him by obeying Allah (SWT).
3. Doing more good deeds and gifting the reward to Imam Al-Mahdi (AS). Pious believers gift all their reward to Imam Al-Mahdi (AS) and other Infallible.
4. Praying sincerely for Imam Al-Mahdi (AS)'s reappearance and keeping it as our first and upmost important need.
5. Preparing ourselves to serve our Imam (AS) in every possible way that we can including serving his followers and lovers and spreading his message to people.
And many other noble acts which can help us in this regard.
Dajjal or Antichrist will be before the reappearance of Imam Al-Mahdi (AS) and he will be killed by Imam Al-Mahdi(AS) or by Prophet Easa (Jesus) by order of the Imam Al-Mahdi (AS).
Part of the responsibility of a leader is to know what is happening to his people. This is especially true for a divine leader (prophet, Imam).
Not all human beings have the qualities necessary to be good leaders. Some people have the social, intellectual, and emotional capacity, foresight, initiative, wisdom, and planning and communication skills to be great leaders. Most people do not. But that is ok, because we only need a handful of great leaders.
So, bearing this burden might be very difficult for the average person. However, the Imam is not an average person. Allah would not give the Imam this responsibility if he did not have the ability to bear it, as Allah says in the Qur'an that He does not burden with something beyond their capability. Because the Imam is at the highest level of spiritual perfection (as well as intellectual and emotional perfection), he has the capacity to handle many things that regular people cannot. Also, when people are truly at a high level of faith and have a deep and sincere connection with God, this enables them to bear things that other people cannot.
Still, of course, we should try our best to give the Imam a good report about our deeds and circumstances, and try to work as hard as we can to improve things around us!
We can not confirm nor totally deny this matter during the Ghaibah of the Imam (AS) as it is part of the personal life of Imam Al- Mahdi (AS) which is kept by Allah as secret and away from the public knowledge.
Some narrations mentioned his marriage and children but our leading scholars did not find such narrations authentic enough to establish a confirmed fact. Many leading scholars openly refused such narrations like Shaikh Al-Mufeed and Shaikh Al-Toosi and Shaikh Al-Bayadhi.
We have narrations refuting the claim of his marriage, such narrations are mentioned in many books like Ethbaat al-Wasiyyah by al-Mas'oodi, page 201, and Al-Ghaibah by Shaikh Al-Toosi, page 134, and Dala'il al-Imamah by Al-Tabari, page 130, and Al-Irshad by Shaikh Al-Mufeed, page 366 (Arabic edition).
We may advise Mo'mineen to leave this personal matter of the life of the Imam Al-Mahdi (AS) to the Imam (AS) himself when he will come back to the public life.
This Hadeeth ( Al-Mahdi's name is the same name of the Prophet and his Kunya is the same Kunya of the Prophet ) is narrated in many Shia and Sunni books. These are few Sunni books:
1. Sunan Al-Tirmithi, V. 3, P.343.
2. Al-Mo'jam al-Awsatt by al-Tabarani , V.8, P. 178.
3. Al-Mustadrak 'ala al-Saheehayn by al-Haakim al-Nisaboori .
And many others.