Who is the first Khalifah of the Muslims?

Who is the first khalifah after Prophet Muhammad passed away and who is the first to follow the rules?

Answer:

The First Khalif of Muslims is Hadrat Abu Bakr (r.a)

Hadrat Abu Bakr was the first to worship and follow the rules of rules after the death of Muhammad(phub) as a khalifah, the first one of the khulafa-i rashidun.
Hadrat Abu Bakr is the first one of free-men, wise khalifahs, ashara-i mubashara to believe in Allah after our prophet Muhammad (asm) started to declare Islam. Hadrat Abu Bakr was a sahaba who was applying what Prophet Muhammad said and obeying the Sunnah more than everyone else. He was the first khalifah who maintained the shariah rules after the Prophet Muhammad passed away.
Prophet Muhammad faced at least a hesitation from every man when he declared Islam but Hadrat Abu Bakr (ra) accepted his invitation to Islam with no hesitation and no doubt saying "It is true if he says so."And Prophet Muhammad made a gentle metaphor saying “Abu Bakr’s iman would be heavier when the iman of the others are put in a scale and Abu Bakr’s iman is in the other scale”.
Hadrat Abu Bakr sacrificed his all life and property for Islam and became a prominent in all good deeds. He never left Rasulullah, beginning from his childhood a strong friendship was connected between them.
Rasulullah preferred Hadrat Abu Bakr's point of view in many cases. Prophet Muhammad was consulting especially Hadrat Abu Bakr in some matters, while he is negotiating important private and public matters. (Ibn Haldun) And Arabs was calling him as