Pieter Wuille is a computer programmer, who is part of the Bitcoin Core development team since 2011.
He is the inventor of the Segregated Witness (SegWit) soft fork concept which was formally proposed to be implemented in Bitcoin as BIP141.
Peter Wuille is also responsible for other significant Bitcoin improvements such as BIP 66, libsecp256k1. He is one of the top contributors to Bitcoin Core client in terms of commits. His Github username is sipa.
Wuille has a Ph.D in computer science and he is co-founder of Blockstream.