ER Spoilers - Hal Holbrook to Guest

Multi-Emmy Award-winning actor and recent Academy Award nominee Hal Holbrook makes a special guest appearance on NBC's "ER" (10-11 p.m. ET) as Walter Perkins, a terminal cancer patient who impacts the life of Dr. Kovac (Goran Visnjic). The episode, "Truth Will Out," will air Thursday, April 24 (10-11 p.m. ET).

During a visit to a hospice ward, Dr. Kovac crosses paths with Walter, who despite his terminal illness, remains upbeat, offbeat and funny -- while continuing to outlive every other patient that comes through the doors of the facility. His presence impacts Luka and affects a major decision in his life.