Pieter Wuille appears as an author across several Bitcoin specifications. Reading those documents is a more concrete way to understand his contributions than assigning any developer ownership of the protocol.
A family of keys from one seed
Wuille authored BIP 32, which describes hierarchical deterministic wallets: a tree of keys derived from a seed. Its public-key derivation capabilities allow some systems to generate receiving information without holding the corresponding private keys.
BIP 32 is a key-derivation design. It is not the same document as BIP 39, which concerns mnemonic recovery words. The BIP 32 specification.
Collaboration on SegWit and Taproot
BIP 141 lists Eric Lombrozo, Johnson Lau, and Wuille as authors. It describes Segregated Witness, including the separation of witness data and the introduction of block weight. The SegWit specification.
BIP 341 lists Wuille, Jonas Nick, and Anthony Towns. It specifies Taproot’s output and spending rules. Those credits identify authors of particular documents; the wider implementations and deployments involved additional contributors. The Taproot specification.
Describing what a wallet actually watches
Wuille and Ava Chow authored BIP 380, the general specification for output script descriptors. A descriptor can record script structure and key derivation information, addressing the problem that possession of keys alone may not tell restored software which outputs to look for. Output descriptors.
Follow the contribution, then the evidence
These specifications let readers inspect an idea, its rationale, and its limits. A document’s author list is not an exhaustive list of everyone who reviewed, coded, tested, or used it.
For the historical deployments, continue with SegWit’s activation and Taproot’s activation.