What is epiphenomenalism? Who is a philosopher who accepts this?
I have provided for you below an excerpt from a discussion taken from "Chalmers' principle of organizational invariance makes consciousness fundamental but meaningless spectator of its own drama" written by Danko Dimchev Georgiev, MD. It describes epiphenomenalism and makes note of a few "epiphenomenalists"
The epiphenomenalism is a sort of one-way dualism, in which consciousness is a product of brain processes but is itself without any causal effect on those processes. The central motivation for epiphenomenalism lies in the premise that all physical events have sufficient causes that lie within the class of physical events. If a mental event were something other than a physical event, then for it to make any causal contribution of its own in the physical world would require a violation of physical law. Huxley  who held the view compared mental events to a steam whistle that contributes nothing to the work of a locomotive. Taking into consideration that the historic roots of epiphenomenalism trace back to nineteenth century it is important to note that under physical in the above statement is meant material (in the following discussion we will revisit both terms).
Nevertheless the epiphenomenalism is absurd; it is just plain obvious that our pains, our thoughts, and our feelings make a difference to our (evidently physical) behavior; it is impossible to believe that all our behavior could be just as it is even if there were no pains, thoughts, or feelings . Also if our souls are attached to the bodies and just 'experience' what the body is doing without having any possibility to react, who decides which soul to which body will be attached? A Universal Marquise de Sad who decides millions of children in Africa to 'suffer' just without any sense?
The clinical practice has not shown mismatch between the experience (e) and the neural events (n) to exist. Neither inverted qualia (e.g. pleasant feeling associated with neural events that normally evoke pain like tachykinin neuromediation), nor dancing qualia (e.g. sudden and unpredictable flipping between pain and pleasure associated with neural events that normally evoke pain) have been observed. Mismatch between the objective reality and the experience is only possible if the peripheral reception is affected i.e. the stimulus elicits neural event that normally must not occur! Such mismatch deteriorates the survival capability ...
This solution provides a description of epiphenomenalism and the name of a philosopher who accepts this view.