Van Rens·se·laer  (vān rěn'sə-lîr', rěn'sə-lər, vän rěn'sə-lär')  Dutch merchant who was a founder of the Dutch West India Company (1621) and established Rensselaerswyck (1635), the only successful privately held colony in America, on his estate in present-day upstate New York. |