What kind of beast is presented in William Blake's "The Tyger"? How it is related to the main theme of the poem?

The tyger is
a "fearful" beast. In the first
stanza, the speaker asks what "immortal hand or
eye" (God) could have created
him. In the fourth stanza, the speaker uses theof God as a
blacksmith
creating the tyger (tiger). Being born of fire and steel, the tiger is, in
Blake's
descriptions, something strong and fierce. In the following stanza,
the speakers asks if the
tiger's creator was happy about his
creation: 

Did he
smile his work to
see? 

Did he who made the lamb make thee? 

The speaker asks if God ("he"), who made the lamb,
also
made the tiger. The lamb represents peace and love. The lamb is often
symbolically synonymous
with Christ in Christian theology. So, the speaker is
asking if God could create something so
loving (the lamb) and yet also create
something so dangerous and ferocious. There are no answers
to the speaker's
questions. This leaves the poem open to different interpretations. Perhaps
God
did make both peaceful and dangerous things in the world to create a
balance and an analogue
with the good/evil dichotomy. Perhaps the tiger (or
other dangerous and evil things the tiger
represents) was created by a fallen
angel, a demiurge, or a devil. The speaker can only
ponder. 

Consider a gross simplification. The speaker asks who created the

tiger and why. This echoes similar questions such as: If God is loving, why did he
create
suffering? Blake goes much deeper in terms of theological and
philosophical questions. But the
general idea concerns how and why the world
contains love and hate, good and evil, peace and

destruction.