Who is Elliot Roosevelt from The Rise of Theodore Roosevelt and what is their importance?

In youth, the younger Elliot seems stronger and more popular than his brother does. However, injury and depression drive Elliot down an endless road of drugs and alcohol. Whn he attempts to leave for France, in an effort to beat his addiction, Elliot leaves a scandal when another woman claims to carry his child. Roosevelt goes as far as attempting to declare his brother insane, to gain access to his estate. Eventually, Roosevelt advises Elliot's wife to leave him and, always a woman of poor health, she soon dies. Roosevelt advises his brother to avoid the funeral. In fit of alcohol-induced mania, Elliot dies at an early age.