Short answers, pulled from the story.
Daulat Khan Lodi was the governor of Lahore from 1500 to 1524 who invited Babur into India and effectively ended the Lodi dynasty. He was the son of Tatar Khan and served as governor of the Jalandhar Doab before being promoted to Lahore. His decision to invite Babur transformed him from a loyal administrator into the architect of a foreign invasion.
Daulat Khan Lodi sent messengers to Babur in Kabul in the year 1523 to offer his allegiance in exchange for military assistance against the emperor. Babur agreed to the proposal and his army quickly captured Lahore and Dipalpur. The alliance crumbled almost immediately when Babur presented Daulat with Jalandhar and Sultanpur instead of the coveted Lahore.
Daulat Khan Lodi defended Guru Nanak from accusations made by his own officials and protected the young spiritual teacher from the Nawab. One of his officials, Jai Ram, was married to Guru Nanak's sister Nanaki and found Guru Nanak employment at Daulat Khan Lodi's store and granaries as a keeper. Two audits found the store fully stocked with correct accounts despite complaints about Guru Nanak wasting the stocks.
The events that Daulat Khan Lodi had started in motion culminated in the battle of Panipat in 1526 where Ibrahim Khan Lodi lost his life. Babur became ruler of India and went on to found the Mughal Empire which would rule the subcontinent for centuries. The legacy of Daulat Khan's actions was the complete transformation of the political landscape of India replacing the Lodi dynasty with the Mughal Empire.
Daulat Khan Lodi turned against the Lodi dynasty because his relationship with the last Lodi emperor Ibrahim Lodi deteriorated into open hostility. Ibrahim was known for his rigid proud and suspicious nature which alienated many of his own nobles. This disaffection drove Daulat to make a decision that would alter the course of Indian history forever driven by personal ambition and fear.