  We present late-time optical images and spectra of the Type IIn supernova SN
1986J. HST ACS/WFC images obtained in February 2003 show it to be still
relatively bright with m(F606W) = 21.4 and m(F814W) = 20.0 mag. Compared
against December 1994 HST WFPC2 images, SN 1986J shows a decline of only <1 mag
in brightness over eight years. Ground-based spectra taken in 1989, 1991 and
2007 show a 50% decline in Halpha emission between 1989-1991 and an order of
magnitude drop between 1991-2007, along with the disappearance of He I line
emissions during the period 1991-2007. The object's [O I] 6300, 6364, [O II]
7319, 7330 and [O III] 4959, 5007 emission lines show two prominent peaks near
-1000 km/s and -3500 km/s, with the more blueshifted component declining
significantly in strength between 1991 and 2007. The observed spectral
evolution suggests two different origins for SN 1986J's late-time optical
emission: dense, shock-heated circumstellar material which gave rise to the
initially bright Halpha, He I, and [N II] 5755 lines, and reverse-shock heated
O-rich ejecta on the facing expanding hemisphere dominated by two large clumps
generating two blueshifted emission peaks of [O I], [O II], and [O III] lines.
