Rashi: This is Esav.

Rashi (15): He is a Rasha; Sug is like "Kesef Sigim" (26:23) - Sigim are the dross, the waste mixed with silver.

R. Yonah: Sug Lev is a stubborn person who always relies on his thinking. He does not heed another's words, to contemplate whether they are better than his own words, and to abandon his own words if the latter prove unlike his own words. He is always satiated from his deeds. His Ru'ach rests in its habits. He sees no lack in his Sechel and Da'as. He is complete in his eyes; he does not need help from another's Sechel or counsel. He finds a contradiction to his words only from his Binah's investigation. However, he never investigates, for he relies on the first matter that came on his Ru'ach first. He does not seek another thought. An investigator, just like he toils mentally to recognize the Emes, he yearns to be helped from others' investigations, and to see which is correct.

Malbim: His heart is Nasug (goes back) and does not agree with his deeds, for he senses that his path is not good - "Lev Yode'a Maras Nafsho" (9). Also when he laughs, his heart is pained. Even so, he is satiated from his ways - so he goes in the path of death, and he will receive his punishment.

Rashi: It is Yakov.

R. Yonah (14-15): He is not stubborn. He takes counsel with people. He is concerned for their words; it is easy for him to hearken to them. He recognizes the Yesharim, and hears their counsel and is helped via their Sechel.

Rashi (15): The Rasha will be above the Tzadik.

R. Yonah: The prefix Mem shows distancing and separation; a good man will distance from Sug Lev, for stubbornness is from an evil heart, and if one does not accept the counsel and words of the stubborn, and hears counsel from people with more Binah, the stubborn will hate him. An Ish Tov distances from being hated [so he distances from such people].

Malbim: Not only his heart goes back - he totally veers from him, and does not do like his deeds.