Sergeant William Matpi (PN417 and later Warrant Officer NG1820) was from Powat village in the Lorengau region on Manus Island, Papua New Guinea.

Matpi was educated at a Lutheran school on Manus Island before moving to Rabaul, New Britain to look for paid work. When the Japanese invaded Rabaul in 1942 he was working for the government surveyor, A.A. Chauncey. Despite two attempts to escape and hide in the bush he was among the 1200 men pressganged by the Japanese and shipped to Gona to work on the Kokoda Tail. He escaped early and joined the Australian and Papuan troops. After enlisting with the Papuan Infantry Battalion he saw service at Buna, Sanananda, Salamaua, Lae, Finschhafen, parts of Madang and the Sepik region and finally Rabaul. He was awarded the Distinguished Conduct Medal for his military service, one of only three Papua New Guinean soldiers to receive the award.

In February 1945, Matpi was among a group of New Guinean soldiers who protested against the inequality of pay and conditions between Australian and native troops in the New Guinea Infantry Battalion. On 6 Feb 1945, a fight broke out at battalion headquarters over the request that New Guinean troops wear their rank on their laplaps rather than arms. At an inquiry into the incident, Matpi stated that Papuan and new Guinean troops were owed equality of pay and uniforms with the Australian troops they fought alongside.

Matpi left the army in 1946 as Warrant Officer Mapti, the highest rank allowed to him within the system at the time.

In 1954, Matpi was part of a Papua New Guinean delegation to Cairns to meet the Queen on her tour of Australia.