Hakulinen served in the Finnish Army in its war against Russia in 1941–1944, spending a lot of his time there on the frontier at the Svir River.
[1] In his school years, Hakulinen knew the lichenologist Veli Räsänen, who encouraged his early interest in lichens.
Räsäsen had lived in the area for years and had studied its lichen flora quite thoroughly; Hakulinen accompanied him on field trips.
[1] After finishing university, Hakulinen worked as a secondary school teacher, first at Isokyrö, but soon later in Hämeenlinna, where he settled permanently.
[1] In his obituary of Hakulinen, his colleague Teuvo Ahti describes him as "an important link in maintaining continuity between the splendid Finnish tradition of lichenology from William Nylander through E. A. Vainio and V. Rasanen to the present".