Complex sentence: The Elder of the Universe known as the Runner claims that this entity existed in the time before the current universe, eventually committing suicide out of loneliness, which in turn created the Infinity Gems and spawned "reality in all its many forms".
Split into simpler sentences: The Elder of the Universe known as the Runner claims that this entity existed in the time before the current universe, eventually committing suicide out of loneliness. A fragment of its being remained and formed the Infinity Gems, which apparently spawn "reality in all its many forms".