Al Nadr ibn al-Harith also known as Mansur b. Ikrima b. ‘Amir b. Hashim b. ‘Abd Manaf b. ‘Abd al-Dar b. Qusayy was an oppressor and tortured many Muslims in Mecca (Makkah). He persecuted Muslims. He was a criminal who had waged war against the Prophet and his community.
Al-Nadir Ibn al-Harith was one of the main proponents who wrote a document along with others to boycott the small Muslim minority by not selling them anything. In a way, starve the Muslims. This is mentioned by the classical scholar Ibn Kathir (1301 – 1373)
“Hisham stated, from Ziyad, quoting Muhammad b. Ishaq, “And when Quraysh saw that the supporters of the Messenger of God had gone to live in a land where they had attained security and where the Negus had offered his protection to those seeking refuge with him, that Umar had accepted Islam and had now, along with Hamza, joined the Messenger of God and his Companions, and that Islam was spreading out into the tribes, they met and decided to write down a document.
This would record their mutual agreement concerning the Banu Hashim and the Banu ‘Abd al-Mutalib. It specified that they would neither marry with them nor offer their womenfolk into marriage with them nor engage in any buying or selling with them. Having agreed to this, they wrote it down in a deed to which they gave their solemn pledge. They then suspended the document inside the ka’ba in affirmation of this.
“The man who wrote out the document was Mansur b. Ikrima b. ‘Amir b. Hashim b. ‘Abd Manaf b. ‘Abd al-Dar b. Qusayy.” Ibn Ishaq said, “He was also named as Nadr b. al-Harith. The Messenger of God (SAAS) said prayers against him and he lost the use of some of his fingers.” (Bidaya Wa Nihaya, by Ibn Kathir, volume 2, Page 30 – 31
Ibn Kathir also mentions that Nadr Ibn al-Harith was one of the main leaders whom participated in the battle of Badr against the Muslims:
“The Messenger of God bowed and prostrated in prayer twice and said, ‘When they spoke the truth you beat them and when they lied you released them! They did speak the truth, by God. They are of Quraysh. Now, you two, tell me about Quraysh!’
They responded, ‘They are beyond that sandhill you can see over on the far side of the valley.’ That sandhill was called al-‘Aqanqal. “The Messenger of God asked them, ‘How many men do they have?’ ‘Very many,’ they replied. ‘How many in number?’
he asked. ‘We don’t know,’ they answered. ‘How many camels do they slaughter each day?’ he next asked. ‘Some days nine, others ten,’ they told him. The Messenger of God concluded, ‘So their force must be between 900 and 1000 men.’ “He then asked them, ‘What Quraysh nobles do they have among them?’
“They replied, ‘Utba b. Rabi’a, Shayba b. Rabi’a, Aba al-Bukhtari b. Hisham, Hakim b. Hizm, Nawfal b. Khuwaylid, al-Harith b. Amir b. Nawfal, Tayma b. ‘Adi b. Nawfal, al-Nadr b. al-Harith, Zam’a b. al-Aswad, Aba Jahl b. Hisham, Umayya b. Khalaf, Nabih and Munabbih, two sons of al-Hajjaj, Suhayl b. ‘Amr and ‘Amr b. ‘Abd Wudd.’
“The Messenger of God went out to his men and told them, ‘This Mecca has thrown at you slices of its very liver!’” (Bidaya Wa Nihaya, by Ibn Kathir, volume 2, page 264)
The following sources shed more light on this person Nadr (Nadir);
“On their way back to Madinah, at a large sand hill, the Prophet (p) divided the spoils equally among the fighters after he had taken Al-Khums (one-fifth). When they reached As-safra, he ordered that two of the prisoners should be killed.
They were An-Nadr Bin Al-Harith and Uqbah Bin Abi Muait, because they had persecuted the Muslims in Makkah, and harboured deep hatred towards Allah and His Messenger (p). In a nutshell, they were criminals of war in modern terminology, and they execution was an awesome lesson to oppressors.” 
Nadhr (Nazr), one of the prisoners of war, was executed after the battle of Badr for his crime of severely tormenting Moslems at Mecca. Musab has distinctly reminded him of his torturing the companions of Mohammad, so there was nothing of a cruel and vindictive spirit of the Prophet displayed towards his enemies in the execution of Nazr as it is made out by Sir W. Muir.
On the other hand, his execution is denied by some critics, like Ibn Manda and Abu Naeem, who say, that Nazr Ibn Haris was present at the battle of Honain, A. H. 8, six years after that of Badr, and was presented with one hundred camels by Mohammad.
Sir W. Muir himself puts down very quietly Nadhir Ibn al-Harith’s name in a footnote (Vol. IV, page 151) as a recipient of one hundred camels at Honain. The same Nadhr-bin-Harith is shown among the earliest Moslem refugees who had fled to Abyssinia. These discrepancies leave no doubt that the story of Nadhr’s execution is not a fact. …” 
 Ar-Raheeq Al-Makhtum – The Sealed Nectar: Biograpghy of the Noble Prophet By Safi-Ur-Rahman al-Mubarakpuri, page 143 – 144
 A Critical Exposition of the Popular Jihad (Original 1885) – Cheragh Ali page 77 – 79