Linked from
The 14 pages that link to Dirichlet L-function, each with the reason it gives.
Euler productBroader topic: Its Euler product incorporates the character values at each prime.
Multiplicative functionRelated: Complete multiplicativity of χ gives this series an Euler product.
Linnik's theoremRelated: Its zeros and values control the prime-counting estimates behind the bound.
Siegel–Walfisz theoremRelated: The theorem’s proof relies on zero-free regions for these functions.