A Twelver Shi'a Imam is a Guide in all religious and worldly matters, and is believed to have been Divinely appointed. A Sunni Caliph, on the other hand, is appointed by a part of the community, and is mostly a temporal ruler, where the Quran is taken to be the only authority in all matters pertaining to religion.

Within Shi'ism, there are various sects that differ over the number of Imams, or path of succession. The issue of who is the rightful Imam has led to the growth of 3 sects within Shi'ism including: Twelvers, Ismailis & Zaidis.

They also differ in some of the definitions of a Shi'a Imam.

[edit] Imams

[edit] Twelver view

Main article: Imamah (Shi'a twelver doctrine)

According to the majority of Shī'a, namely the Twelvers (Ithnā'ashariyya), the following is a listing of the rightful successors to Muhammad. Each Imam was the son of the previous Imam except for Hussayn ibn 'Alī, who was the brother of Hassan ibn 'Alī.

Number	Name	Kunya (title)	Nasab (patrynomic)	Laqab (nickname/epithet)	Known by Twelvers for	Lifespan, in CE
1	^cĀlī (علي)	Abū al-Ḥassan (أبو الحسن)	Ibn Abī Ṭālib (إبن أبي طالب)	Amīr al-Mu'minīn (أمیر المؤمنین) - Commander of the Faithful	The first Imam and the most significant person beside Mohammed of the Shi'a	600 – 661
2	al-Ḥassan (ألحسن)	Abū Muḥammad (أبو محمد)	Ibn ^cAlī ibn Abī Ṭālib (إبن علي إبن أبي طالب)	Al-Mujtabā (ألمجتبی)	Signing a peace treaty to better Islam, greatly loved by Mohammed and along with his brother one of the Masters of the Youth of Paradise	625 – 669
3	al-Ḥussayn (ألحسین)	Abū ^cAbdillāh (أبو عبداللھ)	Ibn ^cAlī ibn Abī Ṭālib (إبن علي إبن أبي طالب)	Sayyid ash-Shuhadā' (سید الشھداء) - Lord of the Martyrs	Battle of Karbala	626 – 680
4	^cAlī (علي)	Abū Muḥammad (أبو محمد)	Ibn al-Ḥussayn (إبن الحسین)	Zayn al-^cĀbidīn (زین العابدین) - Jewel of the Worshipers	Wept for twenty years on the subject of Karbala, the first Imam after the Battle of Karbala	658 – 713
5	Muḥammad (محمد)	Abū Ja^cfar (أبو جعفر)	Ibn ^cAlī (إبن علي)	Al-Bāqir (ألباقر)	Wearing clean clothes and had extremely good character, was the least oppressed of all twelve imams by the caliph of the time	676 – 743
6	Ja^cfar (جعفر)	Abū ^cAbdillāh (أبو عبداللھ)	Ibn Muḥammad (إبن محمد)	Aṣ-Ṣādiq (ألصادق)	A high scholar revered by both Sunnis and Shias	703 – 765
7	Mūsā (موسی)	Abū Ibrāhīm (أبو إبراھیم)	Ibn Ja^cfar (إبن جعفر)	Al-Kāẓim (ألکاظم)	Grew up in prison to be weak and thin	745 – 799
8	^cAlī (علي)	Abū al-Ḥassan (أبو الحسن)	Ibn Mūsā (إبن موسی)	Ar-Riḍā (ألرضا) (pronounced "Reza" by Persian- and Urdu-speakers)	The only Imam to be buried in Iran	765 – 818
9	Muḥammad (محمد)	Abū Ja^cfar (أبو جعفر)	Ibn ^cAlī (إبن علي)	At-Taqī (ألتقي)	Defeated people in debates at the age of 8	810 – 835
10	^cAlī (علي)	Abū al-Ḥassan (أبو الحسن)	Ibn Muḥammad (إبن محمد)	Al-Hādī (ألھادي), an-Naqī (ألنقي)	(To be added later)	827 – 868
11	Al-Ḥassan (ألحسن)	Abū Muḥammad (أبو محمد)	Ibn ^cAlī (إبن علي)	Al-^cAskarī (ألعسکري)	The penultimate Imam, lived almost his entire life under house arrest and yet still preached to people	846 – 874
12	Muḥammad (محمد)	Abū Qāsim (أبو قاسم)	Ibn al-Ḥassan (إبن الحسن)	Al-Mahdī (ألمھدي)	Current Imam, known to be al-Mehdi, the saviour, believed to be in occultation	868 – Present

The Twelvers further believe that the 12th Imam, Muḥammad al-Mahdī, is believed to be in occultation and it is believed will reveal himself on the Day of Resurrection.

[edit] Ismaili view

Main article: Imamah (Shi'a Ismaili doctrine)

The Ismailis believe that the first five of the first six Imams listed above are the rightful successors of Muhammad, but differ as to the seventh, believing that Ismail bin Jafar was the rightful successor to his father Jafar al-Sadiq, and not his brother Musa al-Kazim. It is important to note that Hasan ibn Ali is not counted as Imam by the Ismailis on the ground that continuation of the Imamate can only occur from the current Imam to a male descendant. Since Hasan and Husayn were siblings, the Imamate could not pass from one of them to the other.

Ali ibn Abi Talib (600 CE-661 CE)
Husayn ibn Ali (626-680)
Ali ibn Husayn (658-713), also known as Zayn al-Abidin
Muhammad al-Baqir (676-743)
Jafar al-Sadiq (703-765)
Ismail bin Jafar

The Ismaili line of Imams continues unbroken up to Imam al-Mustansir, where it diverges into the Nizaris - of whom the Aga Khan IV is the 49th and current Imam - and the Mustaalis.

[edit] Zaidī view

See Zaidi Zaidiyya, Zaidism or Zaydism (Arabic: الزيدية az-zaydiyya, adjective form Zaidi or Zaydi) is a Shī'a maðhab (sect, school) named after the Imām Zayd ibn ˤAlī. Followers of the Zaidi fiqh are called Zaidis (or are occasionally called Fivers in the West). However, there is also a group called the Zaidi Wasītīs who are Twelvers.

[edit] Zaidi Imāms

Followers of the Zaidi fiqh recognise the first four Ithnaˤasharī Imams but they accept Zayd ibn Ali as their "Fifth Imām" instead of his brother Muhammad al-Baqir.

Muhammad	Last Prophet
Ali ibn Abu Talib	1st Imam
Hasan ibn Ali	2nd Imam
Husayn ibn Ali	3rd Imam
Ali ibn Husayn Zayn al Abidin	4th Imam
Zayd ibn Ali ash-Shahid	5th Imam

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