Option 1: Qutb-ud-din Aibak - Qutb-ud-din Aibak was not a Khilji ruler. He was the founder of the Delhi Sultanate and the first ruler of the Slave Dynasty.

Option 2: Jalal-ud- din Khilji - Jalal-ud-din Khilji was not involved in killing his father-in-law. He was the founder of the Khilji dynasty and became the Sultan of Delhi after overthrowing the last ruler of the Slave Dynasty.

Option 3: Ghiyas-ud-din - Ghiyas-ud-din was not a Khilji ruler. He was the founder of the Mamluk dynasty and the first Sultan of Delhi.

Option 4: Ala-ud-din Khilji - Correct answer. Ala-ud-din Khilji killed his father-in-law, Jalal-ud-din Khilji, to ascend the throne of Delhi. He was a powerful ruler known for his military achievements and administrative reforms.