  We investigate the roles of major and minor mergers during brightest cluster
galaxy (BCG) assembly using surface brightness profiles, line indices, and
fundamental plane relations. Based on our own sample and consistently
reanalyzed Sloan Digital Sky Survey data, we find that BCGs and luminous normal
ellipticals (LNEs) have similar central velocity dispersions, central
absorption line strengths, and central surface brightnesses. However, BCGs are
more luminous due to their much larger radial extent. These properties result
in a flattening of the Faber$-$Jackson and Mg$_{\rm b}-$luminosity relations
above 10$^{10.6}$ L$_{\odot,g'}$. We use this effect to estimate an amount of
$60-80%$ of accreted and merged light in BCGs relative to LNEs, which agrees
with results from cosmological simulations. We determine the contribution of
this excess light (EL) at each radius from the difference between the surface
flux profiles of BCGs and LNEs. It is small in the center but increases steeply
to 50% at $\sim$3 kpc radius. The shape of these profiles suggests that BCGs
could be formed from LNEs in three major merger processes. This is also
consistent with the mild increase of the S\'ersic indices from $n\approx4$ to
$n\approx6$, as confirmed in merger simulations. We note that minor mergers
cannot be the dominant origin of the BCG's EL because they deposit too few
stars at intermediate radii $r\lesssim20$ kpc. The shape of the EL profile also
explains a detected offset of 0.14 dex of the fundamental planes for BCGs and
LNEs relative to each other.
