Hector is the dutiful son of Priam and champion of Troy. Famed for his fighting prowess, noble nature and dedication to his family, Hector heroically led the Trojan forces in defence of their land, in the war his brother provoked by stealing Helen away and bringing her back to Troy - though he did not approve of this war and criticised his brother's indiscretions, he nonetheless carried out his duty with skill and bravery. (Apart from a few displays of cowardice and temper in the Iliad that the 2004 movie forgets and which make him a more complicated character, but whatever.)
The Trojan war saw Hector take down several Greek rivals, including Patroclus, whose death sparked Achilles to rejoin the Achaean forces and eventually bring about an end to Hector's life. Though Hector dies a hero's death, the cool thing about A Total War Saga: Troy is you get to rewrite the story. You can ensure the good guy wins for once, have Hector triumph over Achilles, defend his city from the greed of Agamemnon, and even ascend to its throne and counter-attack to punish the Greeks for their wrath before returning home to his beloved family.
As the champion of Troy and its foremost defender, Hector's campaign is all about diplomacy and defence. You'll build a network of allies to strengthen the kingdom and your forces. Such allies will give you several buffs that aren't such a big deal while your influence is small, but by the time The Assuwan League collectively controls 60 regions, you get a blanket -20% off army upkeep, +20% campaign movement, and +30 to morale. Pretty crazy. On a more personal level, you'll be competing with your wimpy brother Paris for the affections of your father, King Priam, with the assimilation of Paris's faction and the city of Troy your ultimate reward, leaving you more than equipped to eliminate your family's rivals. Just make sure your brother doesn't steal your thunder.
RELATED LINKS:
Total War Troy Sarpedon guide: start position, campaign mechanics, and unique units
Total War Troy Agamemnon guide: start position, campaign mechanics, and unique units
Total War Troy Paris guide: start position, campaign mechanics, and unique units