The Mad Titan Thanos is well known for being quite literally obsessed with the Marvel Universe's physical embodiment of death, Lady Death, who gives him his most powerful abilities. However Thanos' love for his Mistress of Death isn't entirely one-sided, with Death constantly encouraging Thanos to escalate his murderous behavior to give her more souls. Thanos' close relationship with Lady Death and her realm have given him access to a slew of powers that allow him control over death itself.
Lady Death is a timeless primordial being in the Marvel Universe that appears as a buxom woman with a skull head, often portrayed a silent observer and influence throughout the cosmos. Thanos, the Mad Titan who is part Eternal and part Deviant, has been obsessed with courting Death since she first revealed herself to him when he was a young child on the planet Titan. Lady Death began grooming Thanos into becoming a murderous villain since the first moment they met, and she has constantly encouraged him to become more and more powerful and vicious by dangling love and affection in front of him and then rejecting him at every turn. To help Thanos reach his "full potential" as a universe-destroyer, Lady Death has bestowed several of his most powerful abilities on him.
Thanos has a seemingly unending package of super-powered abilities including super strength, nigh invulnerability, telepathy, and energy projection. He is also known for scouring the universe for all-powerful objects such as Cosmic Cubes or the Infinity Gems so that he can create extinction-level events that will win him favor from Lady Death. Death has granted Thanos many powers over the years, some gifts and some seemingly curses, that have helped make him the Mad Titan he was destined to be. Specifically Thanos' intimate relationship with his Mistress of Death has given him dominion over death, bestowing him with the ability to curse other beings, to control the dead, and become an immortal being.
While none of these powers might sound like curses at face value, Thanos' immortality granted to him by Death is actually a huge slap in the face to the Mad Titan. While Thanos was already slightly immortal being both Eternal and Deviant, Death's gift made it so that he cannot ever be killed regardless of circumstance. Thanos is obsessed with Death and wants to one day die and live out existence in her realm, but Death has formally banished Thanos from the realm of Death, meaning that anytime he dies, Death almost automatically brings Thanos back so that he can continue being her Herald of Death. Marvel Comics has also shown that Thanos has the power to curse other people to a life of immortality, giving Deadpool the "gift" of life after finding out that Deadpool and Death had a romantic interest in each other (yes, really). Finally, in the Infinity Finale it is shown that Thanos is able to control anyone who has ever died, a power given to him by Lady Death which he uses to save the universe from destruction at the hands of Annihulus.
Lady Death is a constant source of frustration and desire for Thanos, and his entire life's mission revolves around courting Death and becoming her consort. Death's gifts have given Thanos the power to slaughter entire worlds, but they have also kept him at arms lengths from his love, banning him from ever becoming a permanent resident of Death's realm. With a terrifying multiversal variant of Thanos, bearing an Infinity Gem Mjolnir and a Black Winter arm, appearing in the upcoming Timeless event the possibilities for Thanos and Lady Death are almost as endless as Thanos' life expectancy.