Dr. Holger is a bestselling author, psychological counselor, and the founder and CEO of the Schlageter Institute.

From 1992 to 2003, he pursued studies in analytical and behavioral psychology, philosophy, theology, sociology, history, rhetoric, and pedagogy in Mainz, Chicago, and Tübingen, earning two Master's degrees and a Ph.D. This was followed by a stint as a couples' therapist at the University Hospital in Chicago, specializing in sexual dysfunction, and as a co-therapist in the closed psychiatric department of Elisabethenstift in Darmstadt.

In 1999, Dr. Holger founded the Schlageter Institute (si), which now operates out of Wiesbaden, Chicago, and Cape Town. This discreet psychological counseling institute specializes in the development of leaders in business and politics and has carved a niche as a global hidden champion. For over 25 years, Dr. Holger and his team have designed and conducted countless international management assessments, leadership trainings, executive coaching sessions, and complex transformation programs primarily for global corporations. More than 250,000 senior executives and C-level executives worldwide have benefited from the services of si, which, under Dr. Holger's leadership, has been recognized as the best European firm in the field of Organizational Psychology.

Acknowledged as one of the most sought-after voices in psychology, Dr. Holger has served as the psychological expert for German public television since 2006, featuring his own radio show and making hundreds of TV appearances.

He is also a bestselling author of various non-fiction books on parenting, psychology, and leadership. In 2018, 20th Century Fox adapted his socially critical book "Unter deutschen Betten" into a film and released it in cinemas.

Dr. Holger serves as a confidant and advisor to top executives in business and politics worldwide. Following two consecutive surveys, he was honored as one of the fifteen best executive coaches by FOCUS and XING in 2018 and 2020.