Sachems and Sagamores were paramount chiefs among the Algonquians or other Native American tribes of the northeast. The two words are anglicizations of cognate terms from different Eastern Algonquian languages. The Sagamore was a lesser chief than the Sachem. Both of these chiefs are elected by their people. Sagamores are chosen by single bands to represent them, and the Sachem is chosen to represent a tribe or group of bands. Neither title is hereditary but each requires selection by the people thus led. Wikipedia
Several Chiefs and Sachems were in regular discussions with the DWIC and the council regarding matters of trading and land rights.
Sachem referred to the paramount chief, whereas a Sagamore was essentially a sub-chief. The position varied depending upon the tribe, but for the Siwanoys (who were loosely organized but part of the larger Wappinger-Mattabesec), each Siwanoy settlement had its own Sagamore, and there was one Sachem (or paramount chief) over the entire Wappinger-Mattabesec.
In many of the Dutch documents and Indian Deeds, we see almost every signer described as a 'Sachem', but only some of them are described as chiefs in the narrative of the document. So it seems that the Dutch colonists may have used the words Sachem, Sagamore, and Chief somewhat interchangeably. Portions of each of the Indian Deeds appear to be an attempt to establish records of hereditary ownership of specific land areas and to document the transfer of that ownership in return for goods.