Straff Venture was a Tineye and the most powerful noble in the Final Empire before the fall of the Lord Ruler. He was head of House Venture, the richest and most powerful of the noble houses, and the father of Elend Venture. He was a Tineye.
Straff was known for his extreme arrogance and dismissive attitude towards skaa. He's notorious among nobles for his unusually high number of mistresses as well as his frequent visits to the skaa brothels. Elend believed that his father visits the brothels because he enjoys knowing that the women will be killed afterwards.
Straff disliked Elend, and would appoint his nephew as his heir if possible. Though hesitant to have his son killed because of his fear of the Lord Ruler, he eventually conspired with House Elariel to have Elend killed. He arranged to have the guards removed from Elend's quarters while Shan Elariel and another Elariel Mistborn, aided by a group of Mistings, attempted to assassinate Elend and his friends, including Jastes Lekal, heir to another Great House–House Lekal. Vin saved them, killing Shan in the process but leaving behind at least one living assassin. Straff had the assassin killed, claiming the man died when he fell through the skylight, keeping his complicity in the attack secret.
On the day of the fall of the Final Empire, Straff and most of the other nobles of House Venture fled Luthadel, in part because of the skaa uprising but also in fear of the Lord Ruler's anger when he hears about Kelsier's destruction of the atium at the Pits of Hathsin. When Elend refused to leave, Straff became eager for him to stay. He hoped the Lord Ruler would take out his anger on Elend and kill him instead.
After the Lord Ruler's fall, Straff took control of the Northern Dominance, House Venture's home dominance. He contacted Elend, informing him that he was coming to Luthadel so that his son may turn over the city to him. A year after the fall of the Final Empire, his army took up position outside the city. With his army are his secret Allomancers, his illegitimate sons and daughters by his various mistresses. Among them is Zane, the only Mistborn among his children.
After Vin defeated Cett's soldiers at Keep Hastings, Cett left the city and retreated with his army. Zane left after setting his father up for assassination by one of his mistresses. Straff killed the woman and was able to take a sample of a drug that he became addicted to, before falling unconscious.
When Straff regained consciousness, he took back command of his army from Janarle, one of his generals. He then ordered a retreat, then turned back to watch while the koloss attack the city. Though he originally intended to attack the koloss army once they were sufficiently weakened and then take the city, he changed his mind. He decides to allow the koloss to slaughter the people and burn the city, then search for the atium once they leave. Straff believed that the city deserves its fate, since it rejected him.
Once Vin was able to take command of the koloss, she attacked the Venture army. Her first move was to kill Straff, splitting him and his horse in two with a koloss sword.