As revealed in “Baahubali – the Beginning”, the ancestors of Kattappa (Sathyaraj) promised to be loyal to the royal family, and so Kattappa is following the footsteps of his ancestors. Baahubali (Prabhas), the emperor of the kingdom, and Bhallala Deva (Rana Daggubati) are in love with Devasena (Anushka Shetty). But Rajmata Shivagami (Ramya Krishnan) warns them that whoever marries her will be exiled.
Baahubali accepts her condition and leaves Mahishmati after marrying Devasena. But Mahishmati is attacked by Kalakeya King’s son and Baahubali returns to save his kingdom. However, this development sparks fear in the jealous and power-hungry Bhallala Deva.
Bhallala Deva thinks that Rajmata will once again make Baahubali the king of Mahishmati after seeing his bravery. The scared Bhallala Deva orders Kattappa to kill Baahubali. The obedient and loyal Kattappa obeys the king’s order stabs Baahubali.
Shivgami has arranged Devesena’s marriage with Bhallaldeva (as he is the elder one.) But Amarendra Bahubali and Devsena fall in love. And have an illegitimate child Mahendra Bahubali. So Bhallaldeva & Bijjala deva forces Shivgami to punish Amarendra as he has set wrong ideals as a king. Katappa knows of the child as in first part it is shown that the child’s feet on Katappa’ s head. But as he has to follow orders, he kills Bahubali. But now Bhallaldeva & Bijjala deva fear that the kingdom might go to Mahendra (the child) so they order to kill the child as well. But Shivgami saves him and realizes her mistake
He said that he did, but he was Ballaldev, who killed Bahubali. But to give throne to Ballaldev (As he was son of Shivgami. As later on she become selfish for her son Ballaldev). Shivgami takes promise Oath from Kattappa to lie and take gilt.
That is why after realizing the her big mistake and sin, Shivgami takes whats remaining of Bahubali Vansh to secure place and finally gave-up life while saving him.
“Kill the first king of every generation in Mahishmati” It is a secret commandment which will be portrayed in the second half of the movie with a backstory of Kattappa’s ancestors.
Kattappa is the one who killed Bahubali’s father, and it’s not revealed to anyone. In a similar fashion, he kills Bahubali, for being the first king of his generation.
Amarendra Baahubali is crowned as King and Bhallala Deva as Commander in Chief. They both fall in Love with Princess of Kuntala Kingdom (adjacent to Mahishmati), Deva Sena. But Deva Sena loves Baahubali. Baahubali insists on marrying Deva Sena but Sivagami denies the marriage and so they both run away from kingdom and leads life in disguise. Then Bhallala Deva is crowned as King of Mahsihmati. Later on Kalakeyas wage a war against Mahishmati and this time Bhalla Deva couldn’t defend his Kingdom. Knowing this Baahubali returns, fights the war and leads to victory. Being jealous of Baahubali from childhood, Bhalla Deva now king of Mahishmati, order Kattappa to kill Baahubali. As Kattappa is bounded slave to throne, he kills Baahubali as per orders and by then Deva Sena delivers Mahendra Baahubali. Knowing this Bhallala Deva orders to kill Mahendra Baahubali. Realizing the mistake she did by supporting her son, Bhalla Deva, Sivagami tries to protect him by running away.
Bhallala Deva would’ve gone to Sivagami and cribbed about he (Bhallala Deva) is her only son and she being her biological mother did not care about him etcetera by not declaring him as the king. But Sivagami being already committed to her promise would’ve expressed her helplessness and would’ve stated the fact that Baahubali is more worthy of the throne than him. This infuriates Bhallala Deva to the core. Meanwhile this conversation is overheard by Baahubali who fears that the relationship between a mother and son will be soured because of him.
So, whenever there is a war again, he orders Katappa to kill him in order to crown Bhallala Deva as the king and not straining the relationship between the mother-son duo as he himself did not have his mother and Sivagami was the only mother he’d known so he wanted her to be without any guilt or inner confict. As Katappa was loyal to the kingdom and supposedly had a soft corner of Baahubali ( him calling him “Mama”, Mother’s Brother and stuff) unwillingly he did as he was told.