Answer: Theodore Roosevelt, President #26.
It has been said that Obama has racked up more debt than all previous presidents combined, and the same can nearly be said of Theodore Roosevelt with respect to executive orders.
The first 112 years of America : 25 Presidents.
The first 25 Presidents : 1262 executive orders.
Theodore Roosevelt : 1081 executive orders.
Keep in mind, Roosevelt didn't even serve two full terms, he was in for 7.5 years. And yes, many of these executive orders were explicitly to do an end-run around congressional authority, just like Obama does. Just like Obama.
In which term did Roosevelt issue more executive orders?
First term: 251 - just two shy of being more than any other president before him.(Grover Cleveland issued 253 - in 8 years. Roosevelt did 251 in 3.5 years)
Second term: 830 - more than 5 times any other president in any single term.
Most of those executive orders were issued in his second term, after he would have no longer been up for re-election - a classic scheme that progressives do. They assault us when they can't be held accountable anymore. Sound familiar?
Here is a table for illustrative purposes.