On 1982 Jan. 9 a brightening of 0.75 mag of the OIafpe star R127 (=HDE 269858) was detected. Subsequently extensive photometric (optical and infrared) and high resolution spectroscopic (ground-based and IUE) observations covering a period of more than one year have been carried out. These observations have shown R127 to be a new S Dor variable which is hotter than any previously detected and studied variable of this class. For its maximum phase we derived the following basic parameters: Mbol = −10.6, Teff = 16000 K, R* = 150 R⊙. The stellar wind is characterized by a small mean velocity (v = 110 km s−1), a high mass loss rate (M = 6 · 10−5 M⊙yr−1), and a decelerated velocity field. The optical spectra show strong Balmer lines with P Cygni profiles. The He I lines changed within the one year period from strong P Cygni type lines to complex line profiles with extremely wide (FWZI = 3000 km s−1) shallow emission line wings. The IUE spectra are dominated by crowded absorption lines of singly ionized metals. A very complex shell phenomenon is indicated by the multiple substructure of these ultraviolet lines. We suggest that R127 is a massive (M > 60 M⊙) Of star evolving via a short-lived S Doradus phase to a late WN star.