Answer:
In "Do not go gentle into that good night" by Dylan Thomas, the speaker compares death to darkness or night. This is an extended metaphor because the comparison is sustained throughout the entire poem.
Example 1: "Do not go gentle into that good night, / Old age should burn and rave at close of day; / Rage, rage against the dying of the light." Here, the speaker is encouraging his father to fight against death and not accept it passively, comparing death to a "good night" that he should not "go gentle into."
Example 2: "And you, my father, there on the sad height, / Curse, bless, me now with your fierce tears, I pray. / Do not go gentle into that good night. / Rage, rage against the dying of the light." Here, the speaker is pleading with his father to resist death and not give in to it, comparing death to the "dying of the light."