Hamlet

Ensign Flandry, CHAPTER SEVENTEEN.

"Exhaustion pulsed through [Flandry] in huge soft waves. To sleep...to sleep, perchance to dream...." (p. 182)

Thus, Flandry quotes from Hamlet's famous soliloquy, as also do:

a kzin in Poul Anderson's third Man-Kzin Wars story, "Pele";

Wanda Tamberly in "The Year of the Ransom."

Hamlet is about being dead. There is a ghost, a skull and this soliloquy - and an endless source of quotations.