What is AES and why is it the current encryption standard?

The Advanced Encryption Standard, or AES, is a symmetric block cipher that replaced the Data Encryption Standard in 2001 after a public competition. AES supports key lengths of 128, 192, and 256 bits, operates on 128-bit blocks, and uses substitution-permutation network rounds. AES-256 is considered secure against all known attacks including quantum computing threats for the foreseeable future. It is the mandatory encryption standard for US government classified information and is widely used in TLS, VPNs, disk encryption, and wireless security.