Wolfert I van Borselen (c. 1245 – 1299) was lord of Zandenburg and Polsbroek and regent for John I, Count of Holland.

[1] Wolfert and his older brother Nicolaas were first mentioned on 6 November 1271 as Nicholaum et Wlfardum filios domini Henrici Wissen militis, fratres[2] On 1 May 1296, Wolfert and his bastard brothers Raas and Jan were mentioned.

[4] In 1276, Wolfert was one of those who sealed a trade agreement between Floris V, Count of Holland and a number of cities in Overijssel and Gelderland.

In November 1282, Wolfert and his wife transferred their allodial lands near Zandijk and their castle Zandenburg to Beatrix of Holland, wife of Floris V. She then granted it back in fief inheritable by sons, daughters, and all other relations.

[8] This act laid the foundations for the power of Wolfert's Van Borselen branch, because it could amass wealth over generations.

By 1284, Wolfert was a knight, when he was mentioned in a charter that gave the traders of Dordrecht freedom of toll for their shipping.

[1][10] In November 1291, Wolfert and his oldest son paid homage to the Count of Flanders in exchange for 100 pounds a year.

[12][1] It was a logical follow-up of the action which had cost Floris' life, i.e., to bring Holland in the English alliance.

She was also the mother of Gerard van Voorne squire to Floris V.[14] However, in time his power gave rise to jealousy.