Matti Rintamäki was born on 4 February 1877 in Kauhajoki, Finland, the son of Matti Korpi-Kyyny (b. 19 June 1844), and Kaisa Sofia Heikkisdotter (b. 3 February 1841). His parents had married 25 June 1867 at Kauhajoki.
His known brothers and sisters were Sanna Kaisa, b. 9 September 1869, Maria Elina, b. 15 December 1870, Juho Nestori, b. 20 April 1874, Herman, b. 25 June 1879, and Adolfina, b. 1 December 1884.
He was a farmer, living at Kyyng farm, Päntäne, Kauhajoki, Vasa County, Finland.
He was married to Maria Sofia (née Mäki, b. 15 July 1879 at Kauhajoki, d. 1947).
They had the following children: Auli Maria, b. 6 August 1898, Viljo Matias, b. 26 February 1900 (d. 1901), Martti Aleksi, b. 12 December 1902, Yrjö Nikolai, b. 20 January 1904, Toivo Aleksi, b. 16 June 1905, Valde Johannes, b. 4 October 1906, Taimi Lyydia, b. 8 November 1907, Helmi Lahja Katariina, b. 15 December 1908 (d. 1910), Vilho Sulo Matias, b. 16 April 1910, Lauri Onni Viljami, b. 29 July 1911.
Matti Rintamäki and his companions were all lost, his body was never found. Later, his widow brought a civil suit in the High Court against the Oceanic Steam Navigation Company (White Star line) for manslaughter and grave neglect. The case was heard on 24 January 1913 and was settled with a payment of £375 in compensation. Matti was his family's only support, and earned, according to his widow, 1500 Fmk ($287/£59 3s) a year.
Matti Rintamäki became a father again, posthumously, when his eleventh child: Eino Aatos was born on 12 November 1912.