The line of imams of the Mustali Ismaili Shia Muslims (also known as the Bohras/Dawoodi Bohra) continued up to Aamir ibn Mustali. After his death, they believe their 21st Imam Taiyab abi al-Qasim went into a Dawr-e-Satr (period of concealment) that continues to this day. In the absence of an imam they are led by a Dai-al-Mutlaq (absolute missionary) who manages the affairs of the Imam-in-Concealment until re-emergence of the Imam from concealment. Dawoodi Bohra's present 53rd Da'i al-Mutlaq is His Holiness Syedna Mufaddal Saifuddin (TUS) who succeeded his predessor the 52nd Da'i al-Mutlaq His Holiness Syedna Mohammed Burhanuddin (RA). Furthermore, there has been a split in the Dawoodi Bohra sect which has led to the formation of Qutbi Bohra sect which was formed and led by Khuzaima Qutbuddin.
What does a Dai-al-Mutlaq do?
manages the affairs of the Imam