Hermanus 'Herman' Jacobus Coster (30 June 1865 – 21 October 1899) was a Dutch lawyer and State Attorney of the Zuid-Afrikaansche Republiek.

During the South African War (1899–1902), Coster joined the Hollanderkorps: a voluntary unit of Boer foreign volunteers consisting of 130 men and which had been established a mere month earlier.

Coster, then a lieutenant, was killed at the Battle of Elandslaagte, along with fellow officer Cars Geerts de Jonge and seven soldiers: P.J.

Another 35 of others were taken prisoner, among them Willem Frederik Mondriaan (brother of the Dutch artist Piet Mondrian).

[3] There are also streets named after Coster in the Transvaal neighbourhoods of Leeuwarden and Rotterdam, as well as in Pretoria in South Africa.

Coster and the Hollanderkorps were featured as part of the exhibition 'Good Hope: South Africa and the Netherlands from 1600' held at the Rijksmuseum in Amsterdam in 2017.