Born in Baltimore, he spent his early childhood in the Latrobe Homes in East Baltimore. He later lived with an uncle, William Kohler, a chief district courts commissioner, and an aunt, Margaret Kohler, a hairdresser, who lived on Cedarcroft Road in the Idlewood neighborhood of Baltimore.
Mr. Kreiner attended St. Matthew School in Northwood and was a 1964 Loyola High School graduate.
He earned a sociology degree at what is now Loyola University Maryland, where he joined the Green and Gray Club, a school spirit organization. Family members said he retained close friendships with the club's surviving members, who will be his pallbearers. He later received a master of business administration degree in finance from Loyola.
In 1967, he met his wife, the former Jo-Anne "Jo" Tillman, while on a winter ski trip to the Poconos sponsored by Loyola and Notre Dame Maryland University.
"Dennis was across the aisle from me on the bus seated with three other girls on a seat designed for two," said his wife, a retired attorney. "He leaned across the aisle and introduced himself." She said they later met again at a Johns Hopkins social event, and he told friends, "That's the girl I am going to marry."
In 1968, Mr. Kreiner joined the Maryland Air National Guard and took tests that enabled him to receive training in electronics at the Chanute Air Force Base in Illinois. After nine months of instruction, Mr. Kreiner reported for duty at the Guard's Martin Airport headquarters, his wife said.
"The members of his unit started laughing when he told them he had been trained as a flight simulator specialist. They didn't have a flight simulator," she said. He later became his unit's information officer and edited The Jet Gazette, the base's newspaper.
He briefly became a city school substitute teacher and then took a clerical job at the old Mercantile-Safe Deposit and Trust Co. on Redwood Street.
"He was a self-made man," his wife said. "He was making $4,000 a year when he started at the bank."
She said he had to persuade her parents to allow her to marry. "They insisted he earn at least $6,000 a year before granting him permission," she said.
In 1970, he joined the management training program at Mercantile and entered the University of Baltimore School of Law. After graduating with a legal degree in 1974, he was the second hire for the bank's in-house legal department. Mr. Kreiner went on to become senior vice president and assistant corporate secretary.
His wife said he helped run the annual shareholders' meeting and board of directors' meetings.
"Dennis was a solid citizen. His manner was confident, and he never got excited," said H. Furlong Baldwin, former chairman of Mercantile Bankshares Corp.
Mr. Kreiner was a member of the American Banking Association and headed its Risk Management Committee. He received honors for his four decades at the bank in April 2007.
"Because he had lived through several transitions of leadership, he was in a unique position to understand Mercantile's role in the greater Baltimore community and in many charitable organizations," his wife said. "Due to his vast knowledge of the inner workings of the bank, he was frequently referred to as 'Mr. Mercantile.' "
He retired in August 2007. Several weeks later, a merger was announced with Mercantile and PNC.
He also taught business law at Towson University for many years.
He was a past president of the Southland Hills Community Association and was vice president of the Greater Towsontown Community Associations. He coached both girls and boys basketball for the Lutherville-Timonium Recreation Council.
He also served on the board of the Catholic High School of Baltimore.
Mr. Kreiner was a Ravens fan and a member of the Antique Motor Club of Greater Baltimore.
"He was passionate about music from the 1960s, especially the Beatles," his wife said. "He felt that 'Abbey Road' album, Side B, was the best music ever recorded."
A Mass of Christian burial will be celebrated at 11 a.m. Saturday at the Roman Catholic Church of the Nativity, 20 E. Ridgely Road in Timonium, where he was a member.
In addition to his wife of 43 years, survivors include a son, Michael Kreiner of Baltimore; two daughters, Alice Kreiner of Gambrills and Wendy Clark of Shrewsbury, Pa.; a brother, Louis E. Kreiner Jr. of Virginia; and a sister, Margie Kreiner Sweeney of Baltimore.