| Datuk Siamang Gagap | |
| Birth Name: | Abdul Qahar bin Mukmin |
| Birth Place: | Kampung Repah, Tampin, Negeri Sembilan |
| Death Place: | Kampung Terusan, Juasseh, Negeri Sembilan, British Malaya |
| Other Names: | Pendekar Siamang Gagap |
Abdul Qahar bin Mukmin (born 1817 - unknown), who is better known as Datuk Siamang Gagap, was a fighter from Seri Menanti, Negeri Sembilan.
As a palace official, he was one of the commanders who supported Tuanku Antah and the Undang-Undang in the Battle of Bukit Putus, as Tuanku Antah fought Tuanku Ahmad Tunggal for the succession of the throne, and defended against British intervention.
He later fought against the British late into the 1870s, earning him his reputation as a folk hero.