Ellison wrote the original screenplay for one of the most famous and
considered among the best of the original Star Trek episodes, The City
on the Edge of Forever - the one where Kirk and Spock have to go back
to 1930 New York City to stop McCoy from stopping a woman from
dying who would delay the US entry into World War II, thus letting
the Nazis have more time to develop the atomic bomb and win the
war, thus totally changing history as we and they know it.

Apparently Roddenberry did not like some of the things Ellison put
in the script, like one of the minor Enterprise characters being a
drug dealer, so he did a major rewrite. You think Ellison got angry
from small insults, just imagine how he felt about having his whole
screenplay rewritten.

http://www.islets.net/film/cityedge.html

He also wrote a treatment for a series in the 1970s called The Starlost,
which bears a resemblance to Robert Heinlein's classic tale Orphans of
the Sky - about a crew on a multigenerational starship who long ago
forgot they were on one and think it is the entire universe - which was
also chopped up by TV hacks and he denied it.

http://www.islets.net/novels/starlost.html

http://www.snowcrest.net/fox/star.html

Maybe he does act like a jerk, but it is rarely the quiet wallflowers who
get anywhere in this world. That may not be right, but until the human
race finally matures, it is the best way to survive for now.