Dino Zei was born in Viterbo, a city with no maritime tradition; he has said he always wanted to be a naval officer and first saw the sea at eleven, at Civitavecchia. He became an engineer and an officer in the Italian Navy, serving with its combat-diver command Comsubin, heir to the wartime units that had used Panerai instruments, and he worked closely with Giuseppe Panerai.
When Giuseppe died in 1972 with no family member to take over, Zei, at his wish, took charge of the business and renamed it Officine Panerai. It was then essentially a supplier to the Navy. Under him it continued to equip the Navy's Teseo Tesei unit and made wrist compasses lit with Traser tritium-gas tubes, depth gauges and other instruments for the divers, as well as other military and industrial instruments; according to a Panerai enthusiast history, watch production almost stopped. In 1985 his team offered the Navy the Millemetri, a 47 mm titanium prototype for depths beyond 1,000 metres, which it did not take up.
As mechanical watches revived in the early 1990s, he turned the company back to watchmaking, drawing on its 1930s and 1940s designs. On 10 September 1993 Panerai presented its first civilian collection, the Luminor, Luminor Marina and Mare Nostrum chronograph, aboard the Navy destroyer Durand de la Penne in La Spezia. A special run made for Sylvester Stallone and worn in the 1996 film Daylight brought attention he had at first been reluctant to seek. With the company in debt, he sold it in 1997 to the Vendôme Luxury Group, now Richemont. He later wrote about Panerai's history and designed watches under his own name for the Florentine brand Anonimo.
Much of the detail on his tenure comes from Panerai enthusiast sources and an interview on the Henkitime blog. Casadi has not verified his dates of birth and death; a December 2025 tribute refers to his passing.