Sensor maker Velodyne Lidar Inc said on Monday its board had appointed Michael Dee as chairman, effective immediately after Joseph Culkin stepped down citing health reasons.

Board member Dee was president and the chief financial officer of Graf Industrial Inc, the special purpose acquisition company with which Velodyne merged in September last year.

The company’s founder and former chairman, David Hall, had written a letter in June to the board calling for the resignation of chief executive officer Anand Gopalan, Culkin, directors Dee and Christopher Thomas. The company had said Gopalan would step down at the end of July.

Velodyne in February removed Hall as chairman and his wife, Marta Thoma Hall, as marketing chief on the grounds of lack of honesty, a charge Marta said the couple was not allowed to rebut.

The company also appointed Kristin Slanina to the board. Slanina has been the company’s adviser for the transportation sector since May this year.