Who was Muhammad ibn al-Hanafiyyah and what was his relation to Ali ibn Talib and Shi’at Ali?

Since we got a little more in-depth on Muhammad ibn Hanafiyya and his possible relations to Ali ibn Talib on being either a spiritual son or physical last class, I decided to look into this and found these three sources on him. One being a Britannica stub on his relation to Ali ibn Talib, while the other two are works on his role in Shia Islam.