Whether they made lessons fun, ignited your passion for learning or helped you through a difficult time, that person was a big part of your childhood you will never forget.
This retro photo gallery shows much-loved teachers at schools around Northern Ireland with their pupils during the noughties.
Perhaps your favourite teacher is among them, or maybe you will spot an old school friend.
What are your happiest memories of your school days? Let us know in the comments section.
1. Groggan Primary School
Teacher Diane Fleming with new P1 pupils Alan Boyd, Naomi Wilson, Samantha Hamill and Tyler Heigh, at Groggan Primary School, Antrim, in 2007 | Other Photo: Other
2. Loanends Primary School
P1 teacher Mrs Watson with some of her new pupils at Loanends Primary School, Crumlin - Sam McDaniel, Tyler Worsley, Lainey Green, Ben Hennessy, Matthew Robinson and Sarah Lucas - in 2007 | Other Photo: Other
3. Iveagh Primary School
P1 teacher Ruth McKinney with some of her pupils at Iveagh Primary School in 2006 | National World Photo: Michael Cousins
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4. Carrick Primary School
Teacher Michelle Shaw with P1 pupils at Carrick Primary School, Callum Maxwell, Eoin Green, Samantha Quinn and Leah McDowell, in 2007 | National World Photo: Geoffrey Cousins