Charles Martel was his natural son (Williamson, David H. Debrett's kings and queens of Europe. Topsfield, Mass. : Salem House Publishers, 1988, pg. 65).
Mayor of Austrasia and Neustria, Pepin of Heristal
Pepin (c. 635 ? 16 December 714), commonly known as Pepin of Herstal, was a Frankish statesman and military leader who de facto ruled Francia as the Mayor of the Palace from 680 until his death. He took the title, Duke and Prince of the Franks, upon his conquest of all the Frankish realms.
The son of the powerful Frankish statesman, Ansegisel, Pepin worked to establish his family, the Pippinids, as the strongest in Francia. He was able to realise his dreams by becoming Mayor of the Palace in Austrasia in 680. Pepin subsequently embarked on several wars to expand his power. He united all the Frankish realms by the conquest of Neustria and Burgundy in 687. In foreign conflicts, Pepin increased the power of the Franks by his subjugation of the Alemanni, the Frisians, and the Franconians. He also began the process of evangelisation of Germany.
Pepin's statesmanship was notable for the further diminution of Merovingian royal authority, and for the acceptance of the undisputed right to rule for his family. Therefore, Pepin was able to name as heir, his grandson, Theudoald. But, this was not accepted by his powerful out-of-wedlock son, Charles Martel, leading to a civil war after his death in which the latter emerged victorious (wikipedia.com)