Western scholars consider Śaṅkara to be its "founder", although Śaṅkara does not present himself as an innovator and his independent fortune seems to have started later on. The earliest opponents of "Śaṅkara's" Vedānta, in fact, rather oppose Maṇḍana's version of it. But at a certain point (I do not know when) the idea has spread, that Maṇḍana was not a faithful interpreter of Vedānta. This might have been a consequence of his being associated with Vācaspati after the creation of two sub-schools of Vedānta (Vivaraṇa and Bhāmatī, the latter having been founded by Vācaspati)
I just found a funny passage in a XIII c. commentary on Śaṅkara's Brahmasūtrabhāṣya:
Vācaspati, on the other hand, following behind Maṇḍana [and] not recognizing the meaning of the Bhāṣya on the [Vedānta]sūtra has refuted the prescription about hearing etc. (that is, he has stated that it was not a prescription); but in this case he had recourse to that prescription. Oh, what an enviable wisdom! To hear [reflect] and [meditate] are the duty (dharma) of the renouncer-stage. Hence, while refuting such a prescription [Vācaspati] is [also] hostile towards the very renouncer-stage. Moreover, if there is no prescription, also the sūtra about the responsible ones, endowed with the four stages (that is, including the renouncers, who would have nothing to do if Vācaspati's interpretation were consistently implemented) would be made incorrect through the word atha. Therefore, let us disregard the chatting of Vācaspati […]
(vācaspatis tu maṇḍanapṛṣṭasevī sūtrabhāṣyārthānabhijñaḥ samanyasūtre śravaṇādividhiṃ nirācacakṣe; atra tu tadvidhim ūrīcakre. aho batāsya pāṇḍityam! śravaṇādīnāṃ ca sannyāsāśramadharmatvāt tadvidhiṃ nirākurvan sannyāsāśramayaiva dveṣṭi; vidhyabhāve ca athaśabdena sādhanacatuṣṭayasampannādhikārisūtraṇaṃ cānupapannam. tasmād vācaspatipralāpam upekṣya […] śravaṇādi vidhito 'nuṣṭheyam, on BrSūBhā 3.4.47)
The commentary is the anonymous Praṭārthavivaraṇa, who has been attributed to Anubhūti Svarūpa. The author often overtly disagress with Vācaspati, thus giving us a glince into real Indian disputes. In fact, disagreements are on critical points of Vācaspati's arguments and, in turn, lead to further developments (Amalānanda defended Vācaspati in his Parimala commentary).
Interestingly enough, the author has to add that Vācaspati did not understand Śaṅkara, for, in fact, Śaṅkara seems also to have denied the status of prescription to the one about hearing/reflecting/meditating on the brahman at I.1.4.