Board of Directors

Prof. Dr. Gunter THIELEN Chairman
Soner CESUR Vice-Chairman & CEO
Oktay ERCİYAZ Member of the Board of Directors

Gunter Thielen (Ph.D.), one of Bertelsmann's former Chief Executive Officers, has both founded and named Arvato.

He studied mechanical engineering at RWTH Aachen University and completed his doctorate in economics at the same university.

He served as a manager at BASF between 1970 and 1976 and as a technical director at the Wintershall refinery from 1976 to 1980.

Thielen, as the CEO of Arvato AG between 1985 and 2001, was also the CEO of Bertelsmann AG from 2002 to 2008. From 2008 to 2012, Thielen served as the chairman of the supervisory board of Bertelsmann AG and the CEO of the Bertelsmann Foundation. In this role, he initiated the internationalization strategy of the foundation and managed excellent business projects that dealt with matters at the interface between politics and business. 

In 2007, Gunter Thielen established The Walter Blüchert Foundation which promotes social participation and stands up for people who are in need through no fault of their own. Today, he is still serving as the CEO of the Walter Blüchert Foundation.

In recognition of Thielen’s leadership of Bertelsmann AG, in 2006, he was awarded the Media Person of the Year Award at Cannes Festival.

In November 2011, Gunter Thielen was awarded an honorary professorship in the Faculty of Economics at the University of Witten/Herdecke.

In 2015, he was awarded the Global Leadership Award by Johns Hopkins University.

Today, Gunter Thielen continues to serve as chairman of the Delta Invest, which he founded.

Prof. Dr. Gunter THIELEN

Soner Cesur, who has graduated from the department of management information systems at Boğaziçi University, has a successful history of being part of the management of prominent international companies in his professional career. Cesur held sales and marketing-oriented managerial positions at Hewlett Packard between 2000 and 2006, he served as sales director and general manager at Sony Ericsson from 2007 to 2010, and afterwards he took senior leadership responsibilities at NetApp, the global leader in corporate data storage and management company, between 2011 and 2013.

In 2014, Cesur joined the Bertelsmann Group as Arvato Turkey CEO and during his leadership the company became one of the Bertelsmann’s fastest-growing organization worldwide. In August 2020, he acquired the Arvato CRM Turkey with a management buy-out, financially backed by German investment fund Delta Invest and changed the name of the company to Mayen. Soner Cesur is currently the CEO and Vice Chairman of the Board of Directors of Mayen, as well as the investor and Board Member of the audiobook platform, Audioteka.

Between 2015 and 2018, Cesur participated in three different senior leadership programs at Harvard Business School and INSEAD and continued his development in terms of digital transformation and board dynamics.

Cesur, who has been honoured with many national and global awards throughout his career, was chosen as one of the “40 Most Influential Leaders under the Age of 40” by Fortune for two consecutive years, in 2016 and 2017. He was also listed as one of the most powerful CEOs under 40 by The Economist.

Soner Cesur, is married and father of two daughters, actively works in the area of education of girls and women's gender-balanced participation in the business world and society, as part of his activities within the companies he manages and in non-governmental organizations such as TÜSİAD, YASED, and PWN.


After successfully concluding a wholesale & export management apprenticeship at the age of 18, he studied business and management at the University of Applied Sciences in Düsseldorf, Germany. Following his successful graduation, he obtained a MBA degree from University of Bradford (UK).

Oktay Erciyaz joined 1995 Preussag AG, one of the Germany’s leading technology and mechanical engineering groups, where he gained his first important career steps and management experiences. He was assigned at a quite early career age to international executive roles and responsibilities in the areas of international finance, accounting and taxation supervising operations in more than 30 countries.

In 2000 he joined Bertelsmann SE, a leading media and services conglomerate in Gütersloh, Germany. He worked around 16 yrs. with Bertelsmann and was assigned to CEO roles and responsibilities in The Netherlands, Belgium, Portugal, Turkey as well he had Senior Vice President / Executive Vice President roles and responsibilities in Corporate Development and M&A at group level.

From 2017 until mid of 2020, Oktay Erciyaz was group CEO of Trenkwalder Group AG, a leading HR Services and Outsourcing company with around 40.000 employees, 200 offices in 17 countries.

Currently, Oktay Erciyaz serves as Senior Advisor to globally leading PE funds, as Investor and Consultant in/for startups, as well as Member of Board of Directors in some of his own investments.

Oktay Erciyaz speaks 5 languages, is driven to engage himself in value creation processes and strategies, likes very much tech-driven businesses, and he defines and declares diversity, inclusion, partnership, trust-based relations as important pillars of an agile and successful corporate culture.