Lich appears as one of the Four Fiends of FF1 and FF9. It resembles a skeletal sorcerer, and thus has powerful magic. However, it is usually undead/zombie, and thus can be vulnerable to fire and healing magic. In Tactics it's a dark-elemental summon.
NOTE: The 'Corse' enemy strongly resembles a lich, but there is a skeleton-type named lich. Both are included here.
Although not really resembling the FF1 Lich, there is a monster called that.
CP: Of the legions of ghosts that cling to this world, the greatest are called liches. When a man dies with hatred enduring, he is rent from his station in life, and given new station in death according to the death of his passion...a testament indeed to the depths of the evil manifest in these kings among the dead.
ATK: Descending Darkness