つもりだった expresses a past intention or assumption. With a verb in the plain non-past form, it means that the subject intended to do something at that time. It often suggests that the plan changed or was not carried out, although this is decided by context rather than by the grammar alone. With a noun followed by の, it means that the subject intended something to be regarded as that noun or meant it in that way. The polite counterpart is つもりでした.