The line of twelve and the Imami school
In the Twelver Shia reading, imamate is the leadership of the community after the Prophet in both religious and temporal matters, held by twelve men of his household beginning with Ali ibn Abi Talib. It is not prophethood and does not add revelation; a new messenger is not sent after Muhammad.
The Quran uses the word imam for a leader who is followed, both for good and for wrong, and speaks of God making imams who guide by His command. Those verses establish that a guiding imamate is a Quranic category rather than an imported idea; they do not by themselves name the twelve, which is why the naming rests on transmitted reports and is presented on this site as such, in the collections that carry them.
Because the twelve are historical figures, questions about their lives are handled through the evidence dossiers, and questions about their teachings through the library and the hadith corpus. Neither is answered from memory: where a source has not been obtained or verified, the page records the gap rather than rounding it away.
Quran
وَجَعَلْنَٰهُمْ أَئِمَّةًۭ يَهْدُونَ بِأَمْرِنَا وَأَوْحَيْنَآ إِلَيْهِمْ فِعْلَ ٱلْخَيْرَٰتِ وَإِقَامَ ٱلصَّلَوٰةِ وَإِيتَآءَ ٱلزَّكَوٰةِ ۖ وَكَانُوا۟ لَنَا عَٰبِدِينَ
And We made them leaders guiding by Our command. And We inspired to them the doing of good deeds, establishment of prayer, and giving of zakah; and they were worshippers of Us.
وَجَعَلْنَا مِنْهُمْ أَئِمَّةًۭ يَهْدُونَ بِأَمْرِنَا لَمَّا صَبَرُوا۟ ۖ وَكَانُوا۟ بِـَٔايَٰتِنَا يُوقِنُونَ
And We made from among them leaders guiding by Our command when they were patient and [when] they were certain of Our signs.
۞ وَإِذِ ٱبْتَلَىٰٓ إِبْرَٰهِۦمَ رَبُّهُۥ بِكَلِمَٰتٍۢ فَأَتَمَّهُنَّ ۖ قَالَ إِنِّى جَاعِلُكَ لِلنَّاسِ إِمَامًۭا ۖ قَالَ وَمِن ذُرِّيَّتِى ۖ قَالَ لَا يَنَالُ عَهْدِى ٱلظَّٰلِمِينَ
And [mention, O Muhammad], when Abraham was tried by his Lord with commands and he fulfilled them. [Allah] said, "Indeed, I will make you a leader for the people." [Abraham] said, "And of my descendants?" [Allah] said, "My covenant does not include the wrongdoers."