Historically, King John has one of the worst reputations of any medieval monarch. During his reign, England lost her lands in France, was heavily in debt and placed under Interdict by the pope. But, looking at John's reign critically, we must not forget that he did at least one good thing: he agreed to the terms of Magna Carta.
This 'great charter' was signed in 1215, the year before John died, and was an attempt at bringing peace to John's barons who were at war with each other. In the Magna Carta, the barons listed their many grievances against the king (and his predecessors) and sought royal recognition of their rights and grievances, like the right to inherit without paying a 'relief,' or fine (Clause Two).
By agreeing to Magna Carta, then, King John did something good for the barons of England. He upheld their rights and protected their social and economic position. But Magna Carta also had advantages for the Church. In Clause One, for example, John agreed to maintain the Church's liberty, particularly on the issue of elections, in which he promised not to interfere. This acknowledgement, then, also made John very popular with members of the English clergy.
Finally, from a historical perspective, King John also made freedom fighters, like the Founding Fathers, very happy. According to historian, Dan Snow, this is because some of the clauses that he agreed to "established the basic principles" of being an English subject. Clauses 39 and 40 are especially important in this context:
"No free man is to be arrested, or imprisoned, or disseised, or outlawed, or exiled, or in any other way ruined, nor will we go against him or send against him, except by the lawful judgment of his peers or by the law of the land.”
Also, “to no one will we sell, to no one will we deny or delay, right or justice.”
King John, then, not only appeared as a good king to his barons and clergymen but also to many future generations who sought freedom from oppression and tyranny.