Do the credentials or titles of authors I cite need to be given?
As the MLA Handbook notes (1.2), a title like Dr. or Sir should not be included before a name mentioned in the text and is usually unnecessary to include in your works-cited-list entry.
You might, however, explain the qualifications of an author in the body of your essay if they are helpful in making your point or refuting a claim:
Although many continue to deny the dangers of fossil fuel emissions, James E. Hansen, a climate scientist and the former head of the NASA Goddard Institute for Space Studies, argues that “[c]ontinued failure to phase out fossil fuel emissions will consign our children to a diminishing existence.”
Hansen, James E. “The Constitutional Right to a Healthier Climate.” The Boston Globe, 9 Mar. 2016, www.bostonglobe.com/opinion/2016/03/09/ the-constitutional-right-healthier-climate/0xTKyK1s5SaD0ne78YqRHL/ story.html.