We have almost confused these as the same. Many times we assign the roles of a leader to a ruler and that of a ruler to a leader.
A ruler (not the ones used to draw lines) is a person at the helm of affairs of an establishment, an embodiment of power and class, a person of the highest standard in hierarchy. One who gives instructions and organize an institution. He is power personified, same as a leader but in a subtle way.
Little difference between a ruler and a leader.
A ruler gives instructions to the best of his knowledge, all he wants is perfection, no minding the stress or strain anyone has to go through. All he thinks about is himself and his achievements, forgetting that he didn't do it alone. He never wants advice from anyone and no one cares question his authority as he wants to be seen as the most powerful person.
A ruler gives instructions and doesn't take ideas from anyone because he feels threatened and insecure. He pushes his subordinates not minding what they might be going through. All he wants is everything to be done the way he wants and how he wants. He is mostly not loved by all, only few who he makes his spies and pay them for information about his subordinates which he pays handsomely for.
A leader on the other hand gives instructions, and ask for ideas from his subordinates, he wants to know of any objections and reasons for the objections. He believes he is still growing and can learn from his subordinates. He does not believe in perfection as he knows everyone is bound to make mistakes. He thinks about growing together with everyone around him, he does not personalize any achievements, he believes in the strength of togetherness. He knows he might be the most powerful person but he doesn't go about wielding his powers.
A leader always cares for his subordinates and their feelings, he doesn't push them beyond their limits as he understands rest. A leader is mostly loved by all except for a few who might feel different about him. He doesn't require anyone to spy on anybody as he is open to ideas, advices and criticisms.
Power tend to sometimes intoxicate and change people. Though with power comes responsibilities but some tend to forget where they started from and want to rule instead of lead. Lead others to become better people and not rule them in any direction of your choice.
The weak looks up to the strong to lead but when the strong decides to rule, the weak becomes weaker and the society becomes imbalance. People are scared to air their opinion as they will feel oppressed by their ruler.
We should all learn to be leaders instead of rulers. Let the strong carry the weak along and not drag them along.