Observations and modeling for the light curve (LC) and spectra of supernova (SN) 2005bf are reported. This SN showed unique features: the LC had two maxima, and declined rapidly after the second maximum, while the spectra showed strengthening He lines whose velocity increased with time. The double-peaked LC can be reproduced by a double-peaked $^56$Ni distribution, with most $^56$Ni at low velocity and a small amount at high velocity. The rapid postmaximum decline requires a large fraction of the γ-rays to escape from the $^56$Ni- dominated region, possibly because of low-density ``holes.’’ The presence of Balmer lines in the spectrum suggests that the He layer of the progenitor was substantially intact. Increasing γ-ray deposition in the He layer due to enhanced γ-ray escape from the $^56$Ni- dominated region may explain both the delayed strengthening and the increasing velocity of the He lines. The SN has massive ejecta (åisebox-0.5ex 6-7 M$_solar$), normal kinetic energy [i̊sebox-0.5ex (1.0-1.5) × 10$^51$ ergs], a high peak bolometric luminosity (rs̊ebox-0.5ex 5×10$^42$ ergs s$^-1$) for an epoch as late as rae̊box-0.5ex 40 days, and a large $^56$Ni mass (raib̊ox-0.5ex 0.32 M$_solar$). These properties and the presence of a small amount of H suggest that the progenitor was initially massive (Mraiso̊x-0.5ex 25-30 M$_solar$) and had lost most of its H envelope, and was possibly a WN star. The double-peaked $^56$Ni distribution suggests that the explosion may have formed jets that did not reach the He layer. The properties of SN 2005bf resemble those of the explosion of Cassiopeia A.