Keyser, 58, of Greencastle, Pa., has worked part time in security at the Western Maryland Hospital Center for one year.
When it comes to getting qualified security help, the Western Maryland Hospital Center doesn't mess around, center spokesman N. Linn Hendershot joked Sunday.
The company has been flexible and accommodating as Keyser travels around the East Coast to attend re-enactments, Keyser said.
Keyser appeared as Grant on Sunday at a weekend living-history event at the hospital center.
After eating some ice cream and greeting some of the patients, Keyser took the stage and spoke about Grant's life.
Later, wearing a T-shirt with bearing a photograph of Grant, Keyser spoke about how his portrayal began.
Keyser, a 1965 graduate of North Hagerstown High School, has been involved in Civil War re-enacting since 1962, he said.
In the 1980s, Keyser repeatedly encountered people who told him he bears an uncanny resemblance to the Union general who went on to become the 18th president. At first, he did not take such comments seriously, but that changed after one friend mistook a drawing of Grant for a drawing of Keyser, Keyser said.
He has been portraying Grant full time since 1995, a role he takes seriously, he said.
Keyser slipped into first person - speaking as if he was Grant - at times during an interview.
Keyser said he likes to dispute some false allegations that commonly are believed about Grant, including that he was frequently drunk while president.
Keyser also refuses to participate as Grant at re-enactments of battles, including Antietam, at which Grant did not fight.
Otherwise, he might be adding further confusion to people's knowledge about Grant's role in history.
Keyser said he already has commitments to appear at 15 events next year, from New York City to Georgia.
While he sometimes receives a fee for his participation, he does not do the work for the money, he said.
Instead, he said he does it because it is a hobby he enjoys. By doing the work, he learns about himself, and also about the American way of life and history, he said.
He also feels that he is helping teach people about what Grant and the Civil War were really like, he said.
"I feel like I am a teacher. I am a history professor," he said.