Utilize the input text as a context reference, choose the right relationship between Dick Costolo and Twitter from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Even as the Street was bemoaning its MAU problems and then-CEO Dick Costolo was trying anything and everything to turn its 500 million monthly visitors into actual users, Twitter bulls could always point to sales growth.

Answer: employer