Sherman Tully is a dermatologist on staff at the Parkview Psychiatric Hospital and a cousin of Louis Tully. The character was cut from Ghostbusters II but some behind the scenes footage and images are found in the Electronic Press Kit and scenes are in the February 27, 1989 script draft. 
Sherman Tully once had a dream that his deceased grandfather was standing at the foot of my bed and was telling him something. Louis claims to have done many favors for his cousin Sherman. He helped Sherman find tax shelters but they were always bad and needed bailing out. He fixed Sherman up with Diane Troxler but ended up giving free dermabrasion for a year.
During the Vigo incident, Louis went to Sherman and asked him to help get the Ghostbusters released from Parkview. At first, Sherman was hesitant because it clashed with his ethics and he could lose his license if he was caught but pointed he couldn't write orders for the psych ward even he wanted to. Louis reiterated Oscar, a baby, was kidnapped. Sherman countered he should go to the police and didn't believe in the paranormal. He looked out his window and saw the Slime Eclipse outside. Sherman agreed to help in exchange for a ride in Ecto-1a. The Ghostbusters suited up and promptly left Parkview. Louis and Sherman were left standing at the curb. Sherman was under the impression Louis was the fifth Ghostbuster. Louis assured Sherman he only helped with the 'big stuff.'
After Louis left New York, Sherman tried to stay in contact but Louis never returned his calls. A few years later, Sherman was surprised to learn Louis was returning for a little bit. He picked Louis up at LaGuardia International Airport and almost immediately asked for help in regard to an investment opportunity he was considering. Sherman then noticed Louis' condition, from Tiamat's meddling, and slowed down. He then advised Louis not too put much thought into the Blood Rain.
Sherman looks and sounds just like Louis.
- Louis' Cousin, Sherman Tully (Deleted Scene)