Gauss introduced the Gaussian integers in an 1832 Latin work named Theoria residuorum biquadraticorum. I believe there is a German translation available. Is there an English, or possibly French translation? If not, is there any exposition of the work available in English in some more modern article or textbook?
Theoria residuorum biquadraticorum was in fact published in two parts. Gauss wrote separate German reviews of many of his published papers and his review for the second part, where he introduces the complex integers, is translated into English by Ewald in From Kant to Hilbert, vol. 1, p. 307 (originally in Werke, 2, p. 169).